I just posted a new blog post about it:
After Penguin hit many web sites, I was contacted by a client who bought my March Of The Penguins course, and he wanted some help with recovering from a really severe "slap" of his money site, which sank like a stone from position #3 for an extremely competitive keyword to position #600 plus. Ouch! In the video I explain why in his case the problem is really bad and very difficult to fix (if at all possible). So for the future, you definitely want to watch the video...
Tiering Your Back Links — Just Say YES! – - Ask Joe FinnAsk Joe Finn