I spoke with Scribd.com yesterday about their partnership with Simon & Schuster to sell 5,000 eBooks in the recently launched Scribd Store, as well as their future plans for where they're taking the business. There are great articles in BusinessWeek and the WSJ on the Scribd/Simon & Schuster deal, so I won't repeat what they cover, but I'll add a few of my own thoughts.
Scribd is tapping into unaddressed needs in the eBook/eContent market by:
Expanding content beyond books. Scribd content runs the gamut of reading material, including things like sheet music, resumes, and recipes in addition to more conventional long-form books, both professional and user-generated. There isn't anything else quite like it on the Web, and nothing like it in an eReader device environment.(Currently, you can download Scribd content into PDF format and sideload them into your Sony Reader, but they don't yet have more streamlined device integration.)
Enabling social interaction around reading. One of the major shortfalls of Amazon's Kindle and Sony's Reader is that they don't support the social behavior that accompanies reading books, like recommending books to others and buying books for a friend. Scribd doesn't take sharing this far, and it isn't yet integrated into any eBook/eReader devices, but at least on the Web it has introduced a social norm around sharing content that eReading has lacked so far.