I commuted for a couple of years on my 24" cruiser a little more than 5 miles each way. Pretty flat commute with the exception of a long bridge in the middle of it that has a bit of a grade. Sometimes I'd have to ride to a meeting and wouldn't have a chance to change, so would be cruising through the city in my suit with my pants pegged. Usually would get a few looks when I did that.

It was definitely more work than riding a larger bike, but I figured it just made for better exercise, and since I wasn't commuting all that far it would be good to make the most out of it. When I lost my cruiser and got a single speed bike it was amazing how much easier the bridges and hills were. I used to pass people on the BMX going up a hill, but only because I tried to keep all the momentum I could, since I was afraid if I slowed down I'd have to get off. When I switched to the single speed a couple of friends who had ridden fixed gear for years and are generally in much better shape than me were really impressed when they couldn't keep up with me on the hills. The SS is faster and easier and I can go longer distances without tiring out (I did 40 miles on a BMX once, but was dead the next day). But it's not quite as fun, particularly when I'm just going into the city or cruising around the neighborhood.