A lot of my friends are "geeks", and none of them have a jailbroken iPhone. In fact, the only person I know who has a jailbroken iPhone is a regular teenager, and that's because he refuses to pay for apps.
For those interested in Bitcoin right now (mostly geeks) I'd say the percentage of jailbroken iDevices is much higher, i'd throw 80% out as a guess.
I think we can all agree that this is reasonable.