At the same time as they revealed the cover of Forza Motorsport 4 (visible below), Microsoft and Turn 10 have revealed that the new racing game will allow you to import your old profile from Forza Motorsport 3. In other words you won't have to start over from scratch, but can keep all your old car designs and get a headstart with free cars, more cash and some other goodies.
There's also a pre-order campaign, which can net you a pack of five different cars - which you can have a look at below. There's also a collectors' edition planned, but it's not ready to be shown off yet - we're guessing that we'll see more of that during E3.
In other words, if it turns out that you cheated on your favorite car from Forza Motorsport 2 in Forza Motorsport 3 you might get punished for it in Forza 4... Or wait, that might have been another game.