Tallbikes are rad because they feel like flying. Plus they are usually janky and danger is fun and cool. Some people ride them on group rides, some people ride them to the grocery store and to work and generally all the time. That's a badge of honor because it is usually not easy to keep a tallbike (or any freakbike) running. They are usually the result of a welder, an hour, two or three frames, and five or six beers.
I never built a tallbike but I built and rode five choppers. For about two years they were my full-time rides. Eventually, all of them broke and I got sick of fixing them. Here is my ten-year-old page about them:
http://ftso.net/bikes/
HH, you ought to enjoy this -- there's a tallbike gang in NY who've had not one, but two in-flight casualties. Both were shit drunk and at least one involved falling off an overpass. I met some of them at Brooklyn Bike Kill in '06, good people.