sugarvalley - I looked at the SERPS thread here and got to May 9th and discounted that date - as I was seeing most of the drop on the 8th and 7th - most of the damage was done well before the 9th on my US site.
As a note both US and UK have almost similar structures - but the UK site seems especially sensitive to algo changes.
Looking at the US site as a 2 dimensional tree - traffic has shifted right and up.
Like you I get most of my traffic long tail, but see higher level keyword phrases popping in and out. The sections hit are probably over optimized, have more backlinks (because they are obviously larger) and really verbose description tags (I probably have the worst description tags in those sectors).
The other things are repetitive text in the anchors and perhaps the length of the text in the snippets I show in the listings (because some traffic seems to have migrated to the twigs on my tree). I changed one section to use distinct anchors, and increased the length of the snippets.
Does anyone know if the 7th and 9th updates were country related?
tedster - I wouldn't discount a Panda update - in the old days the collected the data and then ran it. In real time you would think a change would run on the data on hand and then apply those changes as additional data becomes available.