Hi, I just asked this question on Thursday and got some responses (thread is in General under Hello and Some Questions).

So... for those of us who also have bio kids in the house, it's a little more difficult, becasue we can't let SKIDS go nutty around our bio kids. I'm taking baby steps myself. Here's what I've done so far:

1. I ask DH to "divide and conquer"with me on the weekends that SKIDS are here. For example I'll take the 3 easy kids (BS4, BD13 and SS12) to do some activity while he keeps SS10 (the kind hearted crazy one) at home to work on home improvement projects. Or, he'll take both SKDS out on errands and I'll stay home with BS4 and BD13. Or we'll send the hard one to MIL (lol!). There's no arguing about it because SS10 is really hard, and I'm exhausted.

2. I've stopped doing laundry for the SKIDS, I do all the laundry for the rest of us 4, but SS10 still soils hs pants, so...
3. I've stopped helping with school stuff,, just recently. Because there was absolutely no gratitude, and it's a lot of stuff to remember and organize.
4. I do exchanges to avoid his conflicts with BM, because that really is bad for the kids, but I don't drive them around for school or any activities.
5. I don't discipline unless something directly affects me or my bio kids.

I can't detach completely, because I need to make sure BS4 is safe. SS10 makes idiotic decisions that put him in danger, such as taking off his water wings, so I don't leave them alone together.

I still have a ways to go, but there are more examples on this site if you look around.

I forgot the pros and cons part of your question.

The pros: more energy for my kids, more time for me, less fatigue for me, less fights with DH, less resentment.

oh, I'm also disengaging from BM and MIL--and that has REALLY helped my mood, lol!

The cons: I havent' seen any yet. I'm sure some hubbies (and wives) get pissed off at not having a free nanny, maid and chauffeur for their kids... but really, I don't see how these are reasonable requests.

My SKIDS never even noticed.

This is not exclusive to dads either. I dated a man who had just gotten his second divorce. He had grown kids of his own. He married wife number two, who decided to use HIM as nanny and chef, while she went out partying...

But I think it happens more often to stepmoms because if we have a baby and stay home a bit to take care of our baby, we are naturally expected to take care of the others too. What a miserable time in my life THAT was.

Pros:
* I don't worry about their hygiene, cleaning up after them (if anything left in common areas it gets donated to charity or thrown away), don't have to do their dishes any longer, don't have to buy them food any longer, don't cook for them or help with school lunches, or do their laundry or clean their bathroom, make sure they brush their teeth or act inappropriately (unless we are in public or DP isn't home for some NECESSARY reason).
* Basically, I stopped being their mom at our house.
* Realizing I am NOT their mom and I cannot teach them the basics any longer, I met them at 7 and 9 and they are now 9 (almost 10) and 12.
* I cannot make them do chores or teach them independence if DP or BM don't want to either.
* I cannot spend my money on things for SDs, BM and DP need to figure out when they need socks or underwear or a new winter coat, not me.
* One of my favorite lines: I cannot care or do more than the parents.
* DP can no longer undermine me

Cons:
* I can't say anything to SDs or DP about behavior or needs. It's incredibly hard to walk away knowing the kid is wearing the same shirt/sweater for 5 days in a row because no one but me realizes laundry needs to be done or that showers need to be taken. Or to walk away to the bedroom AGAIN because they are being very loud at 8:30 pm on a weeknight.
* DP gets really tired on the weekends we have them and then gets cranky with me when I refuse to help (like I'm not tired because I'm doing all the stuff you can't do around the house when SDs are with us, like change a freaking light bulb or mow the lawn?).
* Other than the above it's been really nice to STOP doing things...DP is slowllllly starting to realize some behavior problems but has no ability to institute repercussions or the horrible idea of consequences for behavior/actions.

Disengaging from my husband's daughter was the best thing I have done for myself.

Pros: Letting go, for the most part, of anger, resentment and disdain of the situation as a whole. I no longer dwell on her impending arrival. I don't entertain, clean up after, watch her while DH and other family members are unavailable to watch her - if I don't want to. I no longer have to humor SK by acting like I give two shits about her mom and what her mom says/does/buys/how she wears her hair now, blah blah blah when she forgets the house rule that she cannot. My young bio children have 100% of my undivided attention - as they should.

Cons: Aside from my MILs continuous shock and awe behavior towards me that I'd even have the audacity to disengage from her precious snowflake - none.

Pros of disengagement:

- I am no longer asked to watch the kids for DH

- I no longer cook for the kids; DH does it. He used to tell the kids to give me their "food order" and they would shout what they wanted at me. No pleases or thank yous. DH expected me to make whatever they wanted.

- I no longer have to deal with older SS's moods. I would do activities with him like baking or making something and he would get a very bossy and shout at me. I told DH I wasn't happy with the way SS spoke to me and DH dismissed it and said "kids are rude. He speaks that way to his mom and me too".

- I no longer have to feel embarrassed and humiliated when SS would say bye to everyone in the house except me. DH would have to tell him to say bye and he would walk up to me and then say bye to the dog! DH would then excuse SS by saying "he's just shy". Lol! It's funny now, how much that used to upset me. Now I could give a damn. I don't say anything to SS now unless he speaks to me nicely. As soon as I get attitude I say nothing and walk away.

- I don't have to go places with them anymore and feel embarrassed about their behavior. I can't remember the last time I went out to dinner with them. I do my own thing on weekends now and it's great.

- I don't pay for their things now. Last year I paid for half of DH's Christmas presents to them. SS said to DH "thanks dad" and DH just said "you're welcome".

Cons:

- I have to hide everything that belongs to me. DH once gave SS an eraser from my art kit and SS bit it
in half. I have to hide my toothbrush, wash cloths, towels (DH used to give SS my towel too), anything breakable. It's frustrating at times that because I'm not around to watch my stuff it will get damaged.

That's the only con for me.

I only discuss SS behaviors with DH when they affect me, for example constant shouting in the house. Otherwise I leave them to it. I am very happy to be disengaged.

I do nothing for my SD14. She and I do not even exchange greetings or make eye contact when she is here (she lives with us half time). But she still does things that drive me nuts. For example, she mostly stays in her bedroom, unless she's taking very long showers or baths and blasting her music in the bathroom. We only have one bathroom and our house is small. This past weekend, I REALLY needed to get into the bathroom. She was taking ANOTHER long shower, with her music blaring. I knocked on the door. No response. I knocked again and said I needed to get in there. She responded that she was in the shower. I told her she needed to hurry up and get out. Well, she didn't. This went on for a good ten minutes, until I was pounding on the door. Her father finally came upstairs and took the ipod. That got her out pretty quickly. Then she went downstairs and yelled at him about how we don't respect her. Whatever. I needed the damn bathroom.

After she showers, I often find slippery body wash all over the bath tub and she leaves sopping wet wash cloths or hand towels laying in the tub. On more than one occasion, I've slipped getting into the tub because she hadn't rinsed her body wash away after she was done. Also, after she uses dental floss, she throws it on the bathroom floor.

And then there's this. We have a gate at the entrance to our kitchen, to keep the dogs out. She often doesn't shut the gate and the dogs get in there. One day I saw her leave it open. I told her to shut it. She ignored me and my dog ran in there and stole something from the counter before I could get to him. Another day, DH and I came home. We walked into the kitchen. She was in there. The gate was open and one of the dogs had gotten into a bag of nuts. There was a mess all over the kitchen floor. She was completely ignoring what the dog was doing. When her father questioned her about it, she acted as if she had no idea what he was talking about and she walked away.

So yes, I'm disengaged. I couldn't see any other way of doing it. But I really don't know what to do about this kind of stuff.