Interesting story on Babble.com by Lisa Selin Davis about her experience with almost becoming a stepparent.  Plot: woman meets man with daughter, story ensues:

A year later, they moved in, Kim with us three-and-a-half days a week. We kid-proofed my living room. Sometimes, I thought stepmothering included all the parenting unpleasantness without the rewards.....Rich worked funny film industry hours, and I was thrust into an amorphous caretaker role, picking Kim up at school, cobbling together her dinner.

On challenging her soon-to-be husband about her authority regarding the child:

"I have the final say," he told me. "I'll listen to your objections, but in the end, it's up to me."

While I loved Rich's reasonable stance and endless well of love for the kid, I felt a faint sting of rejection, both from him and leftover from childhood. I had thought stepmothering would illuminate my parents' and stepparents' decision-making process. It only made it more confounding. Did my father ever intervene, soften my stepmother's regime? He'd preferred my stepmother to me. I suppose on some level, selfish as it was, I wanted to be Rich's preference.