[IDisposableHero]

If social recommendations didn't work then amazon would have no 'people who bought, also bought...'

The point is, if your business starts off as "we sell books" (and expands to "we sell books and stuff") and you get a lot of users that way, you can mix in some social recommendations on the existing user base and thereby sell more books and stuff.

If your business is "we do social recommendations" you're screwed.