Yeah, i most certainly have Forza 4 as well. Always up for online fun with it, i'm looking at you H.O.T and S.C.G.
It is indeed a great Forza game, most certainly the best i've played and i've played them all. Love the Top Gear addition to the game. In honest opinion, who else did a lap of the track with the "reasonably priced car" as the first thing they did.
When i bought it, GAME offered me a wireless steering wheel as well for £35. Anyone pick it up??.
The cars are unlocked already, you only "unlock" them in career mode. By that, i mean purchase them and upgrade them. Other than that, as far as i know all the cars are in the game and unlocked.