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.
A WebmasterWorld thread and Cre8asite Forums thread has discussion around these "shuffles."
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.
Forum discussion at WebmasterWorld and Cre8asite Forums.

Comments:
Paul Martin
12/07/2011 01:21 pm
Scott Huffman, an engineering director at Google, outlined several updates last week on the Google Inside Search blog. Have a read of it here: http://insidesearch.blogspot.com/2011/12/search-quality-highlights-new-monthly.html Paul
Barry Schwartz
12/07/2011 01:23 pm
I know. I covered that post here.
John
12/07/2011 03:31 pm
More than 50 keywords ranking in the first 2 pages of google from my website vanished from top 100, on DEC 06. However, i still have 10 keywords in the first page. All keywords are similar (50+10), belonging to 20 pages from my website. I have no idea, how to trace what went wrong? :(
SEO Best Tips
12/07/2011 09:27 pm
I've seen some shuffling,but mostly just slow upward trending on my authority sites. I canned all my small content stuff, just not worth the hassle and time.
joshua
12/07/2011 11:20 pm
I have been watching this all Nov - I feel panda / quality analysis algo may be live / and or they are split testing page 1 results and/or freshness
Megan
12/08/2011 10:04 am
Yes we have seen there is an update tat can be seen in searches from dec1 to dec7
David Iwanow
12/10/2011 09:02 am
Ah yep there is certainly a drop across a whole bunch of sites but also noticed a reduction in the number of keywords driving traffic... so more culling of long tail traffic it seems
seo company philippines
12/10/2011 01:57 pm
Whatever the shuffle is, my clients' keywords are getting good ranking! =)
Frases Romanticas
12/11/2011 06:32 am
Well I have Observed Shuffling in My Keywords as Well! It is Quite Hard For Webmasters To Maintain Their Keywords Ranking!
sandeep kumar
12/12/2011 11:19 am
I am not a webmaster and my blog is also relatively new (5 months old) but I saw that in Dec 2011 my site is getting more visitor from google as compared to earlier months.
Rawing
12/15/2011 05:21 pm
i hope my blog back pagerak 3 or 4...because many impact we all needed
Wrinkle cream
12/18/2011 09:09 am
My site decreased in ranking on Dec 8.
Mango Africano
02/13/2012 04:49 pm
Well, yes my site PageRank was decreased because of this update but my visitor amount still remains same.