I write in the YA/Middle Grade market and I've made my living as a writer since 1997 (the year my first book came out). But the key has been diversification. In the first few years, part of the money came from grants, another part from doing school visits, and maybe 30% from royalties. Over the years (and sixteen novels later), it has switched and I tend to make about 70% of my income from royalties (or advances) and the rest from various appearances (at schools, festival, and conferences). And, thanks to ePubbing, all of my works are back in print again. I am hoping that will add to my revenue stream (crossing my fingers, anyway).