Latest Panda update (18 november 2011) was a minor one but still affected a lot of webites badly.
Panda aims at reducing low quality sites (link farms) and improving quality of SERPs.
Many sites like Ezine got adversely affected due to low quality spun content. A site may suffer major drop in rankings if attacked by panda.
To dig deeper, check this:
http://www.keywordcountry.com/blog/g...-panda-update/