While most of the info remains unchanged, bear in mind that Kaplan etc tweak their materials based on changing content on the tests, so if 2006-2007 included additional topics those would possibly be making their way into the 2008 version. Also note that as new drugs are approved or taken off the market these may become fair game or not on the test and so a couple year old guide won't reflect that. That being said, if you can save a lot, go for it -- the majority won't change so quickly.
I recently got the Kaplan lecture notes from someone, but i have no idea what year they are. They seem to be ok. Anyone know if it really matters what year the notes are from?