D90 AF issues?

Trying to decide which DSLR to go for (my first) - having done a lot of research in the last few weeks I've gradually changed from leaning towards the Canon 40D or 50D to a Nikon D90. I like its features and having had a brief look & feel of one in a camera shop I've been reading a lot about the D90 before finalising my decision. I've used a Canon 40D recently which I like but there's just something about the D90 which keeps pulling me towards it.

At the moment my probable choice is D90 with the 18-105 'kit' lens, then add something longer, probably the Nikon 70-300 which is all within my budget. This should suffice for my (hopefully) serious amateur needs - general family stuff, holidays, landscapes and a bit of occasional motorsport action (but not requiring anything more than the D90 will provide re shutter speeds, FPS etc).

My one remaining concern about this choice is that I keep reading the occasional negative comment about the D90's AF, i.e. a bit slow and vague at times, especially compared to Canons. Any views on this being an issue would be welcome please?

I could push my budget and go for a D300 but wouldn't be able to afford a second lens for quite a while. Would have to stick with the 18-105 - which I assume is Ok for the D300? I think that this may be over the top for my needs, unless I really get into of course in which case the D300 could be better?

Not easy deciding is it?