The only potential down side to the excellent Minolta A mount legacy lenses is that it remains to be seen if any of them will be supported by the hybrid autofocus system in the a99. Certainly they should focus OK, like the other Sony and Zeiss lenses that are also "not currently supported" by the new hybrid system. And interesting note here in a press release and description from PhotoclubAlfa about supported lenses for the new AF system:
"For the first time ever, the 19-point AF system with 11 cross sensors is complemented by a multi-point focal plane phase-detection AF sensor. With no less than 102 AF points, this additional AF sensor overlays the main image sensor. Harnessing the power of Translucent Mirror Technology, this unique Dual AF System permits ultra-fast, accurate autofocusing that maintains tracking focus even if the subject leaves the 19-point AF frame.
The α99 also debuts an advanced new AF-D continuous autofocus mode thatís supremely effective with moving subjects. The 19-point AF system provides reliable depth focusing information. Itís complemented by the 102-point multi-point focal plane phase-detection AF sensor that copes effortlessly with subjects traversing the focal plane.
From launch, new AF-D mode is supported by the SAL2470Z, SAL2875, SAL50F14, SAL300F28G2, SAL70400G and SAL500F4G lenses. More lenses will be supported via future firmware updates."
This makes me wonder if older lenses will ever be suported, making their relative value, less.
This is not the case. The point about AF-D is to make focusing on certain SSM lenses (and probably all SSM lenses) faster, not make focusing on existing non-SSM lenses slower. If anything, legacy glass may focus faster because of the upgraded AF system regardless of the specific AF-D feature. The value of legacy glass should not be affected by just this feature alone.