Following after Tim Bray's linking to the Technorati Cosmos for each post, I've done the same. Not that I get nearly the incoming links that Tim does (two orders of magnitude less, in fact).
Simon Phipps makes some excellent comments on the limitations of this approach and has the beginnings of a nice taxonomy of comments.
UPDATE (2004/05/05): Decided to remove the bubblets - I just don't get enough incoming links yet :-). It was a good exercise in making Leonardo a little more extensible, though, and other users of Leonardo can easily add them back in.