Welcome to WebmasterWorld Guest from 18.104.22.168
[edited by: indyank at 5:26 pm (utc) on Jul 5, 2011]
Since I don't see a pattern in this like you do, I am suspecting google's manual tools in play.
I was a panda winner, going from 9 to 4 on our main keyword and getting a bump on most of the long tail. Since that initial bump we have been alternating 4 and 3, then 3 and 2, now 2 and 1.
The simplest way to try to figure out what happened is to set up a spreadsheet...
After about four months my search engine traffic percentage had come back to 80+ (same as pre-panda) but no signs of improvement in the overall traffic yet. Post panda, the SE traffic percentage was around 70 (varying between 69.5 and 70.5).