Absolutely. Even if you only know what people are doing/buying in aggregate, that's still very valuable. And you can still correlate between various anonymized streams of data if you know how they correlate -- i.e. 32-year-old male manga fans are more likely to buy Pokemon and Pocky than average.

Amazon already gets (and uses, vigorously) a lot of this kind of data from Amazon.com, but I'll bet they're salivating at the idea of getting to cross-compare against all the non-Amazon.com data on the same topics. If they're not, they should be.