well, i haven't really looked thru 2007, but my friend did say she saw some errors there that weren't in 2006. but i suppose the reverse is probably true too, i.e. you'll have errors in any edition.
i like the organization of 2007 better, BUT i wouldn't part with my 2006 for anything b/c of the amount of extra space it seems to have. my friend's copy is so full of post-its b/c it doesn't have a lot of extra writing room.