PubSub is doing well over 1 trillion matches a day according to Bob Wyman. Essentially for a couple hundred thousand standing queries against about 14 million sources, watching a big chunk of the blogosphere is eminently doable.
In response to a snarky commenter ("Big deal! Small number of subs, and small number of events."), Wyman jogged me to think about two other things that might make the hype # more interesting: 1) latency between post discovery and completion of matching against all subs, 2) what the heck are people using PubSub for? Other than vanity searches.