In Stuart's words:
Spacebuzz is a toy written by Stuart to test an idea. It displays the currently popular tags used within the astronomy blogosphere. Tags are ranked on the basis of how current they are and how frequently they are used.
The aim is to show tags that are popular across several blogs rather than tags used on a single blog frequently. Repeat tag usage by the same blog is included but all instances other than the most recent have very little weighting.
Brilliant idea, but also a nice way to take a look at who is blogging about astronomy!