Google has recently filed for a patent for their site rank system. This patent filing gives some insight on how the page rank system works. Here is a great article explaining some of the details http://www.buzzle.com/editorials/6-10-2005-71368.asp
One thing I noticed is the lenght a domain is registered for. I typically register domains for only a year at a time. Due to cost, but I will now re-evaluate that.