RedCardinal - 4:05 am on Oct 4, 2012 (gmt 0)
I've looked at around 60 sites affected by Penguin, and there are a quite a few where Penguin only struck particular areas of the site, e.g. main site might be affected, but blog completely untouched. Other cases would be internal pages with very strong links which improved in ranking while the rest of the site tanked.
I think the cases where things have been site-wide probably also observe a very high proportion of bad links to the domain root.
Of course as with most things in search YMMV.