Originally Posted by StephenH

Seems like I saw these links a year or two ago, so they've been around.

I note this quote, though: "Case in point: Carey Rogers, a gent “nearing 60” in Nashville, who bought himself a bike to stay in shape but..." There's a problem there. The reason you can go fast on a bicycle is that it increases your efficiency. The flip side of this is that if you ride at a walking pace, you'll actually use less energy than you would walking. So if staying in shape or getting in shape is part of the desired outcome, you need to be working at it, not coasting around using no more energy than you would sitting on a sofa. And if you coast down to the Sonic and get a nice shake every day, you can probably gain weight doing it. If you really work at it, if you're fat and out of shape, that may mean riding 10 mph, but if you're athletic and in good bicycling shape, then getting a good workout on one is going to involves some speed.

A second consideration is if you have any destination in mind. In randonneuring, I've known faster riders and slower riders, but generally, the "slow" riders just end up not riding period- for them, speed makes the difference between riding with friends or riding solo, and getting in before dark vs after dark, etc. You don't have to be "fast", but being "average" or better really helps.