The short of it: the patent describes a system whereby contextual ads are delivered on a user’s computer using software that lives on that computer – ie a toolbar, a browser, an aggregator, etc.
While the patent is not filed by Google per se, many of the engineers named are employees of Google. This is sometimes done by companies who wish to obscure their intent. No idea if this is the case in this case, but seemingly, this patent covers a potential expansion of Google’s advertising revenue model. It may be, though, simply a way of covering their current model as well. The timing, given the recent settlement with Overture, is interesting in any case.