I think Google has opened a can of worms with Penguin. The problem is... removing links that are nearly impossible to remove. The next thing the spammers are going to do is flood the competing sites with bad back links in order get them penalized so their clients will be equal in being penalized, thus pushing up their own rankings. I think in the long run it is going to get real messy.
Also, I can't verify this but it appears that Google looks the other way with Penguin if the company is spending quite a bit in PPC...
I am by no means an expert but this is how it appears to me.