It's not dangerous in the right place at the right time. I remember being able to ride "no hands" easily as a kid, but only recently starting doing it again (in the right place at the right time), mostly when I'm on my rollers. It depends on my speed and on the bike I'm riding; I've noticed that my Schwinn Super Sport is fairly easy to ride no-handed, but my Bianchi is much more twitchy. My MTB is stable, but has a shaking resonance which gradually builds up until I have to use a hand to steady it.

- Wil