There is an interesting study, recently published, which explored what factors contribute to success in the stepfather/stepchild relationship. (For this particular study they only explored stepfathers, not stepmothers)
It seems the most important thing is making sure the child feels like they can express any concerns they have about the new relationship.
From the NYT Motherlode Blog
You can read the full article here.
Any parents of step-children want to weigh in?
I don't have time to read the whole article and respond right now, but it would be a good idea to cross-post this in the "Blended Families" forum.
One woman in a house full of men: my soul mate: or... twin sons:(HS seniors) ... step-son: (a sophomore) ... our little man: (a first grader) ... and there is another female in the house, after all: our.