@ Steven,
Here's a blog post you might be interested in. Lindsay Buroker (an indie fantasy writer who I've also seen around mobile read) has an e-book publishing blog and wrote an article on 3 indie fantasy authors who are making a couple of thousands a month doing e-publishing:
http://www.lindsayburoker.com/e-publ...-e-publishing/
These folks didn't make it overnight, but it still shows that SF/F genre works aren't "doomed niches" in the e-book world. Everyone's doing different kinds of promotions/pricing strategies, etc. but there's folks out there who are making a pretty decent living out of it.