I found a solution that works, at least on my system, for the very annoying slow downs in Office 2008 for Mac. The biggest issue seemed to be with startup times, taking as much as 30 seconds on a 2.4 Ghz MBP with 4 GB of RAM. Even 2nd run boot times would be slow. The solution for me was to disable any unneeded fonts in OS X's Font Book. I just went through the list and disabled any that looked crazy (do I need the loopy one, or the one that looks like it's on fire?). I ended up disabling at least 100 fonts. After rebooting, you'll launch Word and see "Optimizing Font Menu Performance". After that, you should notice significant improvements. If you run into Keynote presentations, or otherwise, that require a certain font, just go and reactivate it in Font Book. I have cut cold boot times in half and 2nd boot times are a couple of seconds. I hope this helps some people.