I made a mention of this in our December 2011 Google Webmaster report but there is ongoing discussion around this topic.
Some SEOs and Webmasters are noticing shuffles in the Google rankings. We are not sure if they are Panda related or just normal Google flux.
EGOL, a Cre8asite moderator, said:
I watch a limited number of SERPs but the ones that I am watching show a very large amount of flux - compared to what I normally see.
For moderately competitive keywords sites ranking at positions 3 through 10 are jumping up and down the rankings like crazy... and sites that I have never noticed before are flashing in and out of positions 5 through 10.
EGOL rarely talks about Google changes like this, so for him to notice, it might be something.
Some are saying this might be a Panda update but at this point, it is hard to tell.
No word from Google with anything official.