I have put together a few charts, with block activity for the period of February 19 - March 7th. May do more with this data later, tonight.
http://en.wikipedia.org/wiki/User:Aude/adminactivity
My perception that vandalism drops off significantly on the weekends is true. I also recall a sharp increase in vandalism last September when school resumed in the U.S. and other places.
Vandalism is also highest during the day and evenings (in the U.S.), the U.S. is by far the biggest source of vandalism, and schools/universities comprise approximately 1/4 of all vandalism from IP addresses.
I think this means I (and others) need to make blocks of school IPs be for longer duration... the same for other repeat vandals.
-Aude