my dh and I used to do this before we had dd. I used to love it. When we had dd, we got one of the burley carts to pull along the back of the bike, but of course, you can't go on mountain trails! So all our bike riding has since been very tame. Now she is almost 5, and rides her own bike, but lets just say its very slow going...., and of course every time she sees a pretty leaf or rock, she must stop and pick it up, so dh and I get pretty much no excercise, but thats ok.
You have reminded me of all the fun we used to have. There are so many nice trails around here. Maybe we'll get my mom to watch dd and we'll have to have another go at it. It is exciting isn't it?