The Stepmother's Support Group by Sam Baker - read about half of it on the train yesterday coming back from London and I'm absolutely loving it! Looks like it's not out in the US yet, but I'd seriously recommend it. My favourite quote so far (I'm only half way through):

"They call them blended families now"
"Blended? More like liquidised!"

Best of all, the main character goes looking for support on the internet & starts her own blog! You can tell it's written by someone that's really been there, seen it, got the t-shirt, and the issues that get thrown up by BMs & skids are so true.

I've decided that when I finish it I'm going to leave it hanging around the living room, hoping OH will pick it up for a read!

Oh, and she's also written her top ten stepmothers list here: http://www.guardian.co.uk/books/2010/feb/03/sam-baker-stepmothers