This site is worth a post, even if it is implemented as a Java applet.

In a nutshell We Feel Fine tracks blog entries (and pictures) where people mention their feelings, and presents them in various interactive forms…

My description does it no justice, you have to try it yourself.

Update: Like most very cool things, it’s not quite as cool as you want it to be, eg it doesn’t seem to be tracking as many entries as the dots imply (or somehow I keep coincidentally clicking on the same ones). Also, it only seems to track LiveJournal entries. I would really like to see this same thing implemented using Flash (less CPU intensive than Java) and accessing entries from any blog with an RSS feed.