sps, or Slushpile Sleuths, was created for ebook reviews after discussion at the Mobileread forums. (They also wanted a short URL so it was easy to remember & share around away from DW, hence the abbreviation.) It's intended to focus on indie and self-published ebooks, rather than the mainstream ones that get plenty of reviews for the print versions that (mostly) work for the ebook versions.
I expect a lot of reviews about Smashwords books, but Lulu and Feedbooks are also welcome, along with reviews for author releases at their own sites.
Indie ebook quality is hit and miss, and they're scattered on so many different sites that there's no nice simple software to show which ones are read and liked most. This needs people. I had grand thoughts of a template and tagging system and teams of readers coordinating their efforts... apparently, it's not gonna happen like that. At least not right away. I'm perfectly happy with "just throw your commentary about specific ebooks here," and we'll sort out reviewing options later.
So come join sps, and either review the ebooks you've read, even if it's just a link and "I liked this! Hot!" or "Don't waste your time; the typo-monster ate this one," or read what other people have to say and maybe find some gems you would've overlooked.
You can also join ebooks for ebook sources, ereader advice, and conversion tips. Or just grumbling about how your favorite childhood books aren't available as ebooks yet.