Spoiler for 3.07, if you live under a rock.
In the last episode:
Crazy hunter Gordon Walker gets out of the joint, and trades with Bela; an ancient and invaluable hoodoo charm in exchange for information on the whereabouts of Sam. He and some other crazy hunter track Sam and Dean (henceforth: S&D) down and try to shoot them, but Gordon ends up getting nabbed by the vampire S&D were hunting at the time.
The vampire infects and turns Gordon into the very thing he hates most in the world. Gordon escapes the lair, rips the heads off some other newly created vampires, munches on a hapless motorist, and confesses everything to his crazy hunter friend before ripping out his crazy hunter friend's heart.
After this he lures S&D to an abandoned riverfront warehouse, separates them from each other, beats on Sam for a while, until Sam has no choice but to grab some razor wire and wrap it around Gordon's neck and pull until Gordon's head pops riiight off!
S&D have a heart to heart about how much Sam is going to miss Dean when he dies, and Dean starts to teach Sam how to take care of the Impala.