Did you play the demo? has the handling changed since then?
And the tearing?
A bit of a tangent I know but most demo I have downloaded from PSN have bad tearing, Dirt for example, is this erradicated in the final releas of most games and simply a way of maintaining a higher framerate before the game is properly tweaked?
Yes, I played and loved the demo.
I haven't really noticed much difference in the handling, though saying that, I've driven quite a few different cars already, and they all feel different.
I didn't have any tearing in the demo, nor do I in the full game.
As for spinning out and not being able to win races, I've won all my races so far. You just have to use the triggers better. Don't blast the throttle from 0 to max... squeeze it in, and control the spin. I find that going into a big corner, and tapping the handbreak to initiate a spin, then using quarter/half throttle to keep the spin going until the car is facing in the right direction, easing off the throttle to stop the spin, and then reapply up to full, allows you to fly around the corners.
Really great fun

(and a bit frustrating at times too, some of the cars feel more intent on taking you out, than winning the race!)
Vin.
EDIT: Actually there is one instance of tearing, but it's not during gameplay anyway, so I never pay it any attention. The only tearing I've seen in Grid, is just before the race, where it shows all the cars on the Grid, ready to go, and the camera pans around and does a flyby to your car. I get a bit of tearing there, but as I said, none at all during the actual game, so never really paid it any attention.