Linxv5 - 8:46 am on Dec 20, 2012 (gmt 0)
I have exactly the same symptoms on one of our biggest sites.
In my case traffic dropped 40%, exactly the same ammount that all other's report. In this case it was large forum and had 850.000 daily visits from Google before the hit and now it's very unlikely to pass 550,000 daily.
This is the first time that my site got hit by an change, i never had any drop in traffic with Panda or Penguin changes.
I think the same as you, this is related to "low quality content" or not enough content, and maybe it has also some relation with duplicate content, most user-generated content sites will be the most harmed in this round if this is related to this.
Which type of sites were affected in your case? How much dropped the traffic?