Since a couple of weeks I have a nVidia card. Before that I used an ATI card and the thing I liked about it was the regularity of drivers updates that always improved things (one exception with the 10.2 drivers, the first driver in over two years to have problems) and were mostly very reliable.
nVidia makes a mess of regular updates, makes a mess of consistent driver numbers, and is especially bad in removnig bugs that were present in betas, that were reported and widely known and then come out with a 'WHQL' version that contains nearly all the reported bugs from the beta. I have never seen a forum with so many complaints about released drivers, where seemingly nothing was resolved, in the first day of the release. It is a disaster and nVidia would be smart to take all the complaints to heart and do something about it.
For the time being, I advise against this release and continue with the 197.75 driver.
I will reinstal my old 197.75 driver.
Here's a nice overview that someone did about PP CS5 and various nVidia cards and drivers. Note the recent edits concerning the 257.xx series drivers. A couple of words of caution on upgrading nVidia drivers (even WHQL) when they are released. First, nVidia's consumer cards and drivers are geared towards people playing video games and most of the improvements and bug fixes are timed with the release of new game titles. nVidia has a page on it's support website to report bugs, but I suspect that very few people using Premiere are likely to take the time to submit a bug report. If you're using an Quadro card and driver, you are far more likely to be safe in upgrading with a new WHQL driver.
Second, nVidia's driver installer package is notoriously, not very careful about removing all traces of previous drivers. Thus, sometimes, people accidently end up with a "hybrid" driver that is a combination of the new and the old. This is major reason for BSODs, etc.. If you visit gaming hardware sites like Guru of 3D, they suggest that you, uninstall the old driver, use a utility like Driver Sweeper that cleans up remnants of the old driver in the Windows registry, reboot and then install the new driver.
Wow! Is that all worth it? My suggestion (like Harm's) is if you're not having problems with the present video driver, don't install a new driver, just to see what might happen. I'm presently running 257.21 with a GTX 275 and I haven't seen any problems with CS5, but that's just my limited experience. The 257.xx drivers actually corrected an OpenGL problem in Magic Bullet Looks. I suspect that was just by coincidence, since a number of video games also use OpenGL.
Using 257 for a few days now and I haven't experienced any problems with it.