Just finished messing around in Pages, Numbers, and I'll get a chance to play with Keynote later.
I'm liking the upgrades so far.  A bit speedier, nice new templates (even though I doubt I'll use them), and some layout changes.  
One of my biggest gripes with Numbers and Pages was that I had to physically click on File>Export in order to save as a Word, or Excel, document.  Now you can just Save As (CMD+SHIFT+S), so that is super nice.
Either way, I'll definitely upgrade from '08, and probably finally do away with Office 2008.  Ugh, I hate that piece.