Ditto. I have a few sites and some I update once every few months (like adding one page). Another site I add about a page a week. I think it is important to have some updates but I don't think frequency is much of a factor.
ildarius, head on over to the Google forum here, and look for the threads on the Historical Data patent. If you skim through the patent (and the pending associated applications), you'll get some general idea of the factors they look for with regard to scoring with regard to freshness.