@Jonny6 - Toolbar pagerank isn't updated daily. Google's private pagerank is updated daily (at least).
Then every couple of months there's a minor PR update to the *toolbar* pagerank.
Also it's not "less trusted" sites which don't get updated regularly. In-fact many of the recent minor toolbar PR updates have been bringing PRN (N>=1) sites down to PR0. And many large sites haven't seen a PR update since the large major toolbar update in April 09.
So yep, PRIVATE PR is updated daily. TOOLBAR PR is updated for a very small number of sites every couple of months, and a major update is fairly rare (e.g. there hasn't been one in 9 months). It's certainly not the case that TOOLBAR PR is updated daily for trusted sites.