To everyone who has installed Windows 8.1: You need to re-install your graphics driver, even if your graphics driver is up to date. Windows 8.1 has a number of issues with drivers, and many of them were not even compatible with 8.1 at all. From what I've seen and experienced, Graphics drivers are fine once you re-install them.
About Nvidia drivers: it does not actually matter what version of the drivers you are using, as long as you just re-install the driver. I know this from first hand experience (and currently I'm on 334.67 while running 8.1).
If you have special drivers for your mouse and keyboard (such as gaming mouse or keyboard), you might also need to re-install the drivers for those as well. A number of specialty drivers related to specialized equipment, such as music equipment, also required updated drivers. If you have any of that, you'll want to make sure to download new drivers or re-install them.