We've been looking into the issues some people have been finding with the viewer. On the ATI/AMD side, the catalyst 8.9 drivers seem to have resolved a number of issues with the viewer.
On the NVIDIA side, we have also now released on our download page a special version of the viewer designed for NVIDIA GPU's; this viewer has modifications that makes the viewer run much more smoothly and in general and behave better on a broader range of NVIDIA GPU's. If you're curious to run the viewer, please check it out (on our high performance client download page).