Increasing customization/personalization is a key focus for Peter Norvig, head of Google Labs. Presumably, this strategy is designed to create lock-in for Google users (after all, switching between search engines is pretty easy and that low switching cost is, imho, Google's achilles heel. It is also a weakness I think Y! and, more importantly, MSFT are going to target as they try to arrest Google's growth.
To read a really insightful article about Google's future and the presumed importance of creating user lock-in, see Charles Ferguson's excellent piece in Technology Review
