Planet13 - 3:18 pm on May 2, 2012 (gmt 0)

I had a large crawl right before the March 23rd Panda update (which affected one of my sites).

It wasn't on the order of magnitude that you experienced, but it was about 6 times the normal number of pages crawled.

I think part of it was because I was having a canonical URL problem and the same page was being crawled under several different URLs.