I read about this tag cloud web part for MOSS / WSS on bil simser's Fear and Loathing blog, and just installed and tested it. It works with lists (i.e. announcements, events, blogs, etc.), and must be run/configured separately for each list. For me, the executable did not accomplish the final step of linking the tag cloud web part to the tags.aspx page, but using their clear step-by-step directions (written before they had the automatic process in place) I was able to link it on my own. I used it for an Announcements list on a demo portal, and it looks like this (note that it displays tags for expired items, so there are some in the cloud that aren't relevant to what's in the Announcements list):
When you click on one of the tags in the cloud, it goes to a page that looks like this:
Awesome! Fun! Makes a page look snazzy! Makes a blog look like a "real" blog! Sushi bouquet to the folks at WSSSearch.com!