Which recent (i.e. Jan-midFeb 2012) papers and preprint do you consider really worth reading?
References should be followed by a summary saying what is the result and (implicitly or explicitly) why it is important/interesting/insightful/...
One paper per answer (and start from its citation); you can add further but only in the description (e.g.
It generalizes the ides of X in [cite]...).
As it is a community wiki - vote whenever you consider a paper good. Also - feel free to contribute to other's posts.
See Journal club-like thing for a meta post.