If you have a laptop / notebook that uses a GeForce 8 series graphic card, you might want to take concern, as nVIDIA announced earlier last month that they are all potentially defective. More details in this Engadget article below:
Figuring out which NVIDIA GPUs are defective -- it's a lot
Essentially, all every GeForce Geforce 8600M and 8400M chips are affected, so if you have a laptop with these cards, you may want to check with your laptop vendor for a fix. Engadget is also reporting that some GeForce 7 and 6 series laptop chips may also be affected. Dell and HP have already released fixes for affected models.
With this recent announcement, as well as increased competition from ATI/AMD's new HD4000 series graphics cards, nVIDIA's stock took a large beating.