Sadly, in real-world use, the AF in the Tamron 70-200mm f2.8 lens was simply far too slow and inaccurate. Also, from the 150mm-200mm range, my particular lens was useless at f2.8 due to front-focusing softness. So I returned it to B&H Photo and Video (a retailler I recommend).
In its stead, I ordered Sigma's 70-200mm f2.8 EX DG OS HSM. The jury is still out on this one but on initial observation it appears to produce quickly-focused, sharp, blur-free photos at all focal lengths. It is a tad softer at f2.8 and 200mm, but not objectionably so. It also sharpens up nicely all the way to f8, and retains much of that clarity through f11, where the Tamron was dropping off due to diffraction. I think the color and the bokeh might have been a little better with the Tamron lens, as the backgrounds took on more of a washed-out pastel feel, but unfortunately, sometimes the subject did too. This is unforgiveable in a modern AF lens design.
This Sigma lens is double the price of the Tamron though, so this expenditure is not to be taken lightly. It is still a full thousand dollars less than Nikon's VRII. As always, I'll let everyone know what I think of it once I've had the opportunity to photograph more car-sized objects with it. I've got lots of trips planned very soon! Time to get shooting!