So Will Ferrell is a funny guy- no doubts about that. Not only that, but he loves beer, particularly Old Milwaukee Beer. Unfortunately Old Milwaukee is only available in the midwest- which is why I've never really heard of the beer, but I can't imagine that being much different than PBR.
Anyways, he loves the beer so much he did the commercial for free. Which is pretty cool all things considered.
Not as good as this Pabst Blue Ribbon commercial though
Buy Pabst Blue Ribbon, help save America. Drink it ya asshole