Fast lens or slow lens, you can still take good shots. Yes, it is nice to be able to use continual focus and get a high hit rate, but a lot of people will 'zone focus' on a spot where the action is likely to happen....the first bend in motorsport for instance. With a slow focussing lens, that is probably the way to go.
I'd tend to disagree here as a lot of motorsport shots I take involve panning and not static shooting.
Even though the post has gone slightly off tangent, I am learning more here than any magazine has taught me.
Just to give a bit of how I used to play out in the playground. I'd set-up the shot for where I think the best action is and set the camera to 'Auto' (I know, shoot me, but this was how I learned) I then looked at the pic and the info the camera gave on the AV and ISO setting and I adjusted accordingly. When the racing started I then had what I thought was the best shot for that time. Now this is how the day would progress and I'd alter the setting with the movement of the sun, clouds or if I moved spot at the track. I think I have came away with some OK shots (well, they are OK for me, see below)
As said above, the Tamron 70-300mm lens I have is f5.6 at the fat end and the AF is in the body and not the lens. As much as I'd love a Nikon 70-200mm lens (or similar) that's good for f2.8 I can't afford one (not at over £1,000 as I want a shorter lens and possibly a x1.4 or x1.7 TC, then will add a 50mm at a later date etc)
So what about the,D300, Nikon 18-70mm AF-S ED and that'll then leave me with about £600 or so for the best glass I can get for the money.
Next question then, what's the best I can get for around that budget???
EDIT - Edited to add datails on the above shot. ISO200, 180mm, f4.5, 1/250 sec. The image has not been edited in any way other than shrunk and added to Photobucket for hosting.