Someone once told me that bikes were no more exercise than walking. Whoever this was they're an idiot. I know I've gotten back out of shape, but when I first started walking, I could walk more than half an hour. At this point, riding down to the park, which is fairly flat, takes me about 5-6 minutes and gets my heart rate going. I can't really do an entire half hour at one stretch. (Yes, I know, pathetic, but in the beginning a mile seemed like a long way to walk and I built that up to 10 miles a day...)
The worst problem was the seat at first. The first time I was on the bike, it was for about twenty minutes and for three days my butt was sore. Not just uncomfortable, but total I-am-in-pain, sore. So, I went out and got a bigger seat yesterday. It was a vast improvement. I went out earlier and while I'm a little sore, I'll bet I woudn't be if I hadn't started out sore from the other day. So, hopefully, that's fixed.
Yes, it's true you never do forget how to ride a bike, but I'm a bit wobbly on the thing. Fortunately, riding to the park involves quiet, side streets. I'm still not ready to ride on any streets where there might be more than 1 car per minute going by me.