I absolutely love this idea...
http://inventorspot.com/articles/webcycle_makes_internet_users_work_out_32197
A pair of investors found a way to link up a bike machine (similar to what you'd find in a gym) to your computer and linking the rate at which you bike to the internet bandwidth available. The faster you bike...the more internet bandwidth you have to play with...
The Webcyle
It would be even better if you could set your own benchmarks - ie...instead of limiting bandwidth, I "earn" a set amount of hours of internet service per day if I hit my workout goals.....
That would absolutely get me out of bed every morning to go to the gym.
I always thought laptop keyboards should be able to absorb the energy released when typing to charge their battery....random separate thought...