I've been thinking about getting a "motorized bicycle" - somewhat as a toy and also as a bit of a crutch when I don't want to take the bus. (now that I'm about sell the car)

I've never owned a motorbike but I find early 1900's bicycle/motorbike hybrids uber cool. Take a look at this page and tell me those aren't pure sex on wheels:
http://home.planet.nl/~motors-20th-century/drawings.htm

See also: http://www.motorizedbikes.com/
and http://freespace.virgin.net/stones.ukp/triumph.htm

You COULD pedal those ones if you wanted to bike. Or if you ran out of pocket change for the fuel...