I didn't update regularly CSS Zibaldone for several months (from June 2008 to October 2009). Result? My page rank decreased from 6 to 5. Nice lesson. Anyway, I also noticed that the top search queries decreased significantly during this period. Another thing to focus on is the fact that some sections of my site didn't change in content since the beginning. A couple of days ago I started publishing my notes on CSS (in Italian), but Google seems to ignore the newly published content (it has high specificity, though). This section, in fact, is one of those parts that didn't change since now. Lesson learned: update regularly your site, or your page rank will remain low.