Blogrunner demonstrates the ends to which watch engines can be put, in monitoring what the blogospheres are saying about The Gray Lady. Tools like these are increasingly within the horsepower of low end computers and the storage is chump change. Someone's going to come along and shrink wrap this stuff, or turn it into an elegant hosted web service, and all heck is going to break loose.
Technically it's just an aggregator, so there's no reason you couldn't pull similar tricks for individuals.