Thanks guys - I must admit I like the Porsche one too.
Nath - what Joe taught me is that it's all about the correct technique and you have to be prepared to bin a lot of your shots. I took about 350 on the day and ended up with about 20 that I would consider good - maybe that's coz it was my first attempt? Here's what I learnt:
Use shutter priority at around 1/200th - 1/250th (the slower you go the better blur you'll get but it becomes harder to keep the car sharp) and set the AF to servo. Pick a point on the track where you want to actually shoot the car, pick it up in the view finder early, follow it round and when it is at the place where you want to actually take the shot, release the shutter. Here's the important bit - keep following the car after you've taken the shot, follow through kind of like a golf swing. The idea is to match the camera swing (or panning speed) to the speed of the car, so if you have the camera stationery as you release the shutter the car will be blurred. The other thing is to stand relaxed and not tense, try and pan in a smooth action. I hope that makes sense! The shots above were taken on my first attempt using this technique so I hope to improve my success rate over time.
Oh one other thing, the angle of the shot is created by angling the camera, not by cropping in PS.