One thing I noticed when doing a compare-and-contrast of Technorati's stats on blog posting volumes was the subtle change in focus used by Dave Sifry between the figures posted in February and the most recent ones this month.
In his latest column, Sifry claims geek power as being the big driver of blog activity recently. He claims the two big spikes in the last six months are both related to Apple launches: one for the kind-of-video iPod and one for the Intel-based MacBook Pro. Yet, rewind to February, and those spikes are labelled as "Iraq Constitution" and "Alito Hearings" - both clearly political events. A smaller spike once linked to the "Secret CIA Prisons" furore now goes unlabelled. Then the pitch was: "The blogosphere reacts to world news events". I guess the figures can mean just what you want them to mean.
Update: Constantin Basturea has produced a composite of the two graphs to demonstrate the difference more clearly. Thanks for that.