I'm a grad student so most of my riding is back and forth to the local library to study. I use my bike for most of my errands:post office, market, video store, bank, take-out food, etc. Mostly suburban streets with some busier center of town areas. It sounds crazy, but riding seems faster than driving a lot of the time and I get to be outside and get some exercise.
I recently got back into riding (rode a lot in my teens). I needed exercise, but I couldn't stand going to the gym. I tried biking again although I was worried it would aggravate my chronic back problems. I have been pleasantly surprised to find that biking is one of the only things that relieves the back pain. A quick ride and everything feels great. I also really like being able to not drive for most of my basic errands--good for me, good for the environment.