I had a piece of flash fiction published in 100 Voices. I was new to publishing and had yet to get paid for a story, so I was excited at the time, but I wouldn't submit to them again. The piece was about 900 words. I ended up getting about $10 in royalties. Since then, I have been in anthologies that pay advances between $10 and $50. Only one has earned royalties beyond the advance. While its not bad for an early publication, or as a last resort for a story you would otherwise post on your blog or keep in your "trunk," I'd either stay away or think of them as a last resort.