Two wheeled vehicles are almost always superior to four wheeled vehicles (The exception here). I've felt this way since I got my first bicycle. When I was a kid, I would ride my bike up and down the street in front of my house for hours. I also rode it to school every day, except in winter. I would ride for miles, once I was older, to the point that I rarely needed a ride from my parents - even in winter in Minnesota.
It's something I still enjoy, though I'm less likely to ride back and forth on the same street for very long.
You might have noticed the recent increase in gas prices, especially if you watch TV news (tangent: stop watching that crap - blow up your TV). Well, I have some great news for you all: Errands within a mile of your house can be completed faster on a bicycle than in a car or on a motorcycle.
Think about it for a second - with a car, you've got to get in, start it, turn on the stereo and the A/C, put in a CD/select something on your iPod, get out of the parking spot, and then hit many stop signs/stop lights on your way to your destination, then you got to park, and repeat when you're ready to head home. It takes more time than you think.
With a bicycle, on the other hand, you hop on, and start riding. You can adjust your speed to avoid red lights and it's very easy to use smaller roads you wouldn't want to deal with (because they're "slow") in a car. I can ride my bike to the local library and back in less time than it takes to get the car there and parked.
Last night I rode my bicycle to the grocery store I like, which is about 2 miles from my house. There are closer stores, but they suck. The whole trip, including the shopping, took me about half an hour. I might have cut five minutes from that by taking the car, if I was lucky with the stoplights, but I wouldn't have had nearly as much fun.
Fun? Oh yes, it's OK to have a good time when using your bike for "serious" errands. Personally, I tend to cut through neighborhoods I like, and ride "off-road" as much as possible. Plus, bicyclists (and motorcyclists) usually are able to park right next to the door at the establishment they stop at. It's nice.
A lot of the thrills of motorcycling are the same for bicycling, just at a slower (and quieter) pace. I'm not about to give up my Triumph, but I sure do like my bicycle for short trips.