I saw this article from Sunday's NYT calling out the stigma of writing YA material. Writer Margo Rabb, a YA author herself, talks about the experience of having her intended-for-adults novel picked up by a YA publisher. Sympathy from those who consider publishing in the YA milieu "less than" ensued.
I can't tell you how many times I've had people ask me about my work, hear that I write for the children's market, assume a stance of concerned pity, and then express a sincere hope that, someday, I'll be able to make the crossover into (insert implied modifier "real") writing for adults. Happens all the time. And it makes me laugh.
Not that I have anything against writing for adults. I'm no genre-classification bigot. But what's so awful about making your way writing for the younger set? Can't think of a single thing!