Just got home from an 8 mile ride today. I went on a nice multi-use path near my house. It's built on an old railroad line so it's wide, relatively flat and pretty smooth. The 8 miles just flew by and I was nowhere near as tired as I was riding the hills around my neighborhood. I think I'll just try to push it a little further each time.
This sure beats the heck out of walking. Riding bikes is actually pretty fun. Who knew?