Google recrawls Main Web Index every 2 weeks
 

According to an interview Rand Fishkin posted on SEOmoz this week, Matt Cutts claims that Google recrawls the Web (as represented by their Main Web Index) about every 2 weeks. I can infer much from that but won't say more here.

The Supplemental Results Index (which, in my opinion, represents most of the Web) seems to be getting rebuilt maybe once every 2 months, give or take. I'm still not sure about that.

As part of their discussion, Rand asked Matt how much of the Web actually changes. Matt referred to a very old study that concluded the average half-life of a page is about 45 days, but he said that today there are still "tens of millions of pages" that change frequently (while many others change rarely or not at all).