AlyssaS - 4:14 am on Jun 9, 2011 (gmt 0)
According to my log I found and zapped the spam on 19th May (the site had dropped in rankings on 9th may which is consistent with panda 2.1). It got crawled a few days later. And I kept re-checking the cache and the cache date kept getting updated.
I think there was a re-gen of sorts starting late on 6th Jun, it's consistent with the serps upheaval reported in many places. But of course I might be completely wrong and the delay in the site getting back was something else.
But zapping the spam was all I changed - I didn't add any content or amend the structure in any way.