Here is another example of how the NXT can be so much more than just a toy. A group of researchers from Technical University of Denmark and the IT University of Copenhagen have built a robot that goes in the direction that you look.
Here's how it works; You sit in front of a computer that has sophisticated eye tracking software (that's right, it knows where you're looking!) It then sends commands via wifi to a robot that has it's own laptop. This laptop then calculates how much power needs to go the motors, and sends appropriate commands to the 2 NXT's onboard. These then drive the motors appropriately. A webcam connected to the laptop streams back video of where the robot is travelling.
I'm thinking it might be possible to bypass the onboard laptop completely, and have the main PC send commands directly to the NXT. You could then put on a cheap wireless video camera to give you the robot's point of view.