Actually, I'm pretty sure Google already does that, in a way. If you're logged in to one of Google's systems (like Gmail), it knows what you've searched for before, and uses those data to compute your search results, so that if you've done lots of searches on computers and such, computer results get a higher weight. IIRC they do some weighting based on location as well.

Incidentally, I would really, really like to know more about how Google's algorithms work. I'm pretty sure those methods being known would be a great boon to research in those areas of computer science.