the low quality content sucker still i don't know how it is done but Google has done it. and i think its the strictest part of the Update.
There's around 500 updates that Google have been rolling out this year as part of the Panda update. Low quality content is definitely the target though.
The duplicate content mostly.IMO the idea behind Panda was to move all the sites that copied content away from the serps. The ones without content too.