[Jedd]

Sure, but the big problem is not so much the tracking (IP, agent, cookie, etc) but the small number of data points.

To properly evaluate the quality of the data you can get out of a recommendation system, you need to put a useful amount of half-way decent data into it.

It's a relatively small cost to create an account -- it took me less than 30s, most of which was recording a new set of credentials in my password store.

One possibly intentional side-effect of requiring even a very simple registration process is that it may reduce the amount of cruft going into the engine. </speculating>

[amazon_not]

All that is all good and well, but for two things:

- it took me less time to input enough ratings to get useful recommendations than to register

- the registration asks for unnecessary information

Solution: if you don't want cruft in your dataset throw away recommendations not linked to a registration. If the users finds the recommendations useful, offer to save the profile by registering.

It's not like you are going to get any less cruft by forcing users tonregister. The only difference is that you are going to end up with a lot of throwaway accounts.