Okay, so I actually picked up the 2008 and have been transferring my notes over from the 2006 (argh). I debated about doing this for a while, thought it would be useless to buy the 2008, but all in all I'm happy I did. There seems to be more info in the 2008, a lot of things being "extra info" that I had written in my 2006, but generally I would have to say that the 2008 offers more explanations for things.
One caveat--this is based on the biochem section. I haven't gotten to anything else yet.
Does anyone else find that if you go through things really thoroughly, it takes like, forever.