Recently, I observed large jumps in the PubSub LinkRanks for jtauber.com and attributed it to influential sites coming in and out of the 10-day window PubSub uses.
However, in a comment to Trevor Cook's entry on the jumps, the PubSub CEO responded:
The reason for the sudden shift is that we increased the granularity of how we measure linkranks. Specifically, we added individual blogs from the various hosting services for the first time (e.g. livejournal.com/johndoe) - that has suddenly shifted everyone's ranking. Bob Wyman, our CTO, dropped 30,000 places (much to his chagrin). Check out his blog for more details - http://bobwyman.pubsub.com
While it has obviously affected some blogs in the downward direction, I've been sub-50,000 ever since.