I haven't sold any to Amazon shorts, but I have sold several to Fictionwise. Their contract only runs for 7 years, which seems pretty long now that I'm a couple of years into it. The first year I made some money on them, though it doesn't add up to big bucks with the tiny royalties they have on stories. But it's sure been dribbling in since then. But getting to see my name over Michael Connelly's on the bestseller list was worth it, even if it only lasted for weeks, and his name is probably still there, while mine is not.
Kris