Social tagging – user tagged searching

There are several places that let you define a URL and tag it with interests. Is there a service that lets you tag all or part of a web page? Maybe just an image? Why do we trust a Google with that when humans can do it better?

Imagine reading an article at BusinessWeek where a quote is given by Bill Gates. Wouldn't it be nice if you could select the quote, then tag the quote itself as a quote from Bill Gates? Then later, people looking for quotes from Bill Gates would see that quote.

Chris added that you could give the users of the site the ability to label the trust of the tags in a +/- format. A + indicates that the tags are correct, a minus that they're not. Obviously items with higher levels of integrity would float to the top.

Anyway, just a morning idea. More to come I'm sure.