I found Office 2007 Beta to be excellent, and had I kept on my Windows machine, I would certainly have upgraded - after just a few hours of playing with it, returning to Office 2003 was difficult.
But having now switched to Mac, and faced with the prospect of paying again for Office, I've opted for Nisus Writer Express for my word-processing needs, and I think I can get by with Google Spreadsheets for the other part of Office that's sometimes been useful to me.