This is pretty... uh... interesting. Check out the plans for the Goucher College Library.
Treadmills in the library? I supposed that it is not a bad idea because one of the most important parts of mental retention is to exercise - get the blood flowing. The logistics would be a nightmare - electricity, noise control, and how do you prevent someone from sweating all over the books? Though, I always go to the gym with a magazine - is that really so different?