I like to cruise on my 20" bmx. It's pretty much all do with it right now, honestly. Great for getting around campus.

If your heart is set on 20" wheels, make sure you get a good size toptube and a long seatpost. It's really not that bad at all, except if you've got a lot of hills to climb. I'm 6'1" or so, and I usually ride mine about 6 miles a day. The pros outweight the cons, for me anyway.