This is purely speculation, but a lot of people have been talking about it recently, based on some reports of webpages with calendars (basically, dates appearing on the page) suddenly getting more frequent Googlebot hits. Is Google working on a calendar system? Perhaps a search for some subject could bring up a little notification at the top of the results with There is a such-and-such event on such-and-such date. I dunno, they could make some nifty uses for it.

Although Google is bound to release some sort of calendar searching eventually, I don't think that the proposed evidence points to that. More likely, the Googlebot is programmed to understand that webpages that contain dates are more likely to be updated frequently (as in news sites, weblogs, etc.) and so it should check more frequently. It's already known that Google will checked frequently updated pages more often. Dates appearing on the page may be part of this equation. In fact, I'm near certain of it. I've noticed for a while now that pages with dates tend to get more attention than ones without.