One interesting thing is that the paper and my classmates says recommender system on a (conceptually) single server.
Particularly, many students picked Amazon.com as their interesting recommender.
Amazon.com not only offers on-line shopping, but also provide search engine and product info such as release date. I think such a multi-functionality enables Amazon.com to provide approximately good recommendation.
Payal mentioned an interesting idea of recommender for recommender system.
It is a kind of meta-moderation, which is implemented in slashdot system and is one of the very keys of its success.
I think Jon's statement "No. I'm info overloaded as it is!" is on the same meta-level.
Dipti wrote "Yes, I have used pull-technologies like google search engine and also systems like Amazon.com." My question is whether Amazon.com is push technology or pull.