I'm on a livejournal community that shares ebooks and while I don't download all of them (because seriously who has the time?) I'm exposed a much wider variety of books than I am visiting my local library. Though if I'm looking for something specific I'll go to to IRC but for testing out new authors LJ is where I go.
Also, I really do not like to buy DRM ebooks at all. I never like the formatting and with LRX there is nothing I can do to make my ebook look better and Mobi..well it's still work and technically illegal to crack the DRM there as well.
Also, I can't for the life of me find an affordable copy of any of Storm Constantine's ebooks...so just saying ebook stores have their work cut out for them to get someone like me to spend money there.
Baen is the only ebook store I visit and spend money at regularly.