Penguin went mainly after sites that over optimized anchor text, I believe if you're anchor text is in the region of 60%, then you were penguined.
This also goes for on page seo, but Panda also focused on this.
A lot of my sites got hit, as I bought seonukex services a good while back... it's pretty contrivercial, as, what's to stop your competition link bombing the hell out of you.
I've always relied on free traffic, but I'm now looking into paid, I'm sure Google will make a lot of money from penguin... myself, I'm looking at adcentre, at least you can talk to a human, they warn you if you're doing something wrong, and it's a lot cheaper.