FranticFish - 7:26 am on Aug 25, 2010 (gmt 0)
Be sure to read P1R's explanation in that thread on how the Twitter nofollow links ultimately get followed
Whoops! Missed that on first reading. Sorry for the misinformation.
They always did crawl those links, the nofollow attribute only removes the destination link from the Google link graph when calculating value.
Matt Cutts in 2007: "for Google, nofollow'ed links are dropped out of our link graph; we don't even use such links for discovery"