I just bought a D5000 and have 30 days to return it, so as I was reading about the differences between this model and the D90, I see that the D5000 does not have TTL FP capabilty which let's you shoot at varying sync speeds. So what will I not be able to do with flash that the D90 can and is it worth upgrading to the D90 for it (it also has DOP plus of course the body focus motor)?

I am happy with the D5000 as it stands, I should mention that I did purchase an SB600 flash unit at the same time so I could take advantage of this with a D90 if I decide to go that way, but I don't know if it's a compelling reason to spend the extra $$ on the D90.