I have run some unscientific tests with my Tamron 70-200mm f2.8 and Tamron 90mm f2.8 on the A500 before selling the A700. Those 2 lenses were my worst AF performers on the A700 and A300. I focused on vertical wood blinds and between them into my back yard from different distances to get AF to hunt. The A700 went the wrong way reliably every time while the A500 got the blind or the trees in my back yard in focus pretty much dead on with no hunting.

The A700 AF system only seemed to benefit from a higher torque motor than the A300 with otherwise unchanged algorithms and the same tendency to run all the way to the near focus end stop and then go back for strong defocus. The A500 does indeed behave differently, almost never hitting the near end stop, finding focus very quickly. So hunting is thankfully much reduced. Tracking seems to be about the same for the A500 as the A700. Under most practical circumstances the A500 AF system beats the A700 IMO.

My complaints about the Tamron 70-200 hunting are pretty much gone. The lens is just about perfect now.
This was posted by 9000AF on Dixum but I doubt he will mind me reproducing it here. As there are several users of these lenses here I thought it was of particular interest especially as I have been critical of the slow AF of the 70-200mm in the past, although it still may not address the issues of low light focusing (not limited to Sony models).

It's good to know that Sony are not sitting still and have improved the AF algorithm in the A500/550 (presumably the A4xx as well) and it bodes well for the A7xx replacement although I'll be disappointed if there isn't a new AF module as well as software enhancement.