At the moment neither ATI or Nvidia is doing a very good job of providing drivers that will allow SL to run well under Windows Vista. While it is still early days yet, and such driver may be forthcoming, what does Linden Labs plan to do if they are not? OpenGL support seems to be an afterthought, and may never be implemented to a level that provides a reasonable performance for Second Life (which has a lot of difference from regular 3d application due to use of prims instead optimized meshes/models)
It's all very well to say "the graphics companies need to support OpenGL" but that won't satisfy your userbase, and the onus will be on LL to provide a working client. How does LL plan to address this problem?