Scribd.com has certainly evolved quite a bit over the years.
Initially it started out as just a document sharing site, similar to Slideshare, but now gives you the ability to access not only documents like premium ebooks, sheet music, and audiobooks…but also the ability to publish and sell access to documents you to distribute and get exposure for.
It has enormous potential for online marketers, which I believe is still largely untapped, as well as quite a bit of value for users, for quite a bargain.