But seriously, try doing 40 to 60 miles on a mountain bike. Now that is some seriously great excercise!

The longest I've done off-road is 104km -- that was in the Gatineau Hills, in Quebec (near where mlord lives). A friend of mine had told me about a ride to "the firetower", which was about 50km. I thought I'd try it. 4 hours into the ride, with no idea how much further it was to the firetower, half a bottle of water remaining, and one powerbar, I figured I'd better turn around. On the way back, I had to fill up my bottles from a stream. I passed a Pizza Pizza close to home, and ordered a pair of larges to be delivered. I ate slightly more than one of them. Turns out that the 50km was starting from the ski-hill in the middle of the park -- it was a 10km ride for me just to get to the park.