I'm watching 2 sites that have seen a decent reduction in Google referrals since around 24 Jan or thereabouts. Both now down 35-40%.
One site was hit by original Penguin, and had shown some very tentative new life since Dec 2012. Back to absolutely crushed now.
Other site has only a handful of clean natural links, no images, no ads and only ~15 pages of non-commercial content. Only thing that we found was a newly added UserEcho forum for feedback which had a site-wide link to this second site which was invisible to users (a problem in UserEcho).
My guess is something Penguin related came out. Trying to find more affected sites to take a look at.