So nearly the entire month of September has come and gone, and still no new pro-level Nikon camera anouncements. I am impatient! Are Canon and Nikon playing a game of "chicken" to see who goes first and who steals the thunder?
I'd also like to point out that we are just in the infancy of digital photography at this point. Advances in sensors will likely bring about vast increases in the total megapixel count in just the next few years. The elimination of the Anti-Moire filter (also called anti-aliasing) will likely point out all of the flaws in our current lenses. It should also make capture rates much faster as the on-board processors won't have to do as much work, increasing battery life and reducing heat output inside the camera body.
This is an exciting time to be a photographer. If anyone is curious, I currently only recommend a few cameras; the Nikon D300S, D700, and D3/D3S, and the Canon 1D mkIV, the 1DS mkIII and 5D/5D mkII. These are cameras with superlative processing in-body, making for incredibly sharp and colorful photos. The 7D doesn't make my list due to a slightly stronger anti-aliasing filter which softens the output a little too much for my preference. These bodies also use software trickery to reduce chromatic fringing most evident in older lenses. Don't believe me, browse Flickr and search for combinations of D200 and 50mm f1.4D. The staggering amount of blue fringing you'll find at the edges of bright/dark transitions really cut down on the clarity, color, and contrast of the photos, especially when compared to the same lens on a D300 or D700 body.
As with all of my comments, your experience may vary, but this is what I've observed, and one of the key reasons I'm not in any rush to replace my D300. The only useful gain I can make is to go to a D700, because the contrast and clarity of the bigger pixel sites on the full frame sensor, and its better resistance to heat-induced color-noise makes it THE body for Nikon users at this moment. I can only see wanting a Canon 5D mk2 if I were making films and wanted to precisely control depth of field on a budget. The doubling of megapixels really increases the color-noise in low light, and to me, photography is all about capturing colorful photos in low light!
Afterall, why spend all that money on lenses with the ability to resolve 90 line pairs per millimeter if you're just going to stick them on a body with a cheap anti-alising filter or no chromatic fringing reduction software on-board? Ansel Adams used to point out how any modern lens is appropriately corrected at f8, and he was right! However, only the best lenses are useful at f2.8 and below, and it is those lenses which are needed for low-light situations. Car photography is inherently a low-light (or controlled light) type of art. So... pick the body with the best low-light capability for your budget (for me it's the D300 at this point) and lenses which are "appropriately corrected" for use in low light, with larger apertures, and have at it now, before you get any older!*
*All of this advice will likely be out of date as soon as the new Nikons and Canons arrive! LOL