In my mind a bikeable city is one that
1.) Has plenty of bike lanes
2.) Uses a grid street pattern to spread traffic out instead of routing all traffic though main "collector" streets
3.) Uses measures to make vehicle traffic more difficult. IE: speed bumps, one-way streets, car-free streets.
carfree.com has an interesting plan for a car-free city, it's basically a
6-lobe design each lobe being interconnected by light rail.
Pretty interesting stuff, if only I could come up with the money to found my own city...