[nhoernig]

Hey man, I'm also a musician in Japan.
People play on the streets quite often and it'll depend on which station you do it at. Some stations don't ever have people playing. I don't know if that's because of laws or what-not but you never know.

There are a few bars in Shibuya and such that offer Open Mic nights. There are also a few jam sessions in the area.

Check out Cozmo's Cafe, Ruby Room (listed above) and 7ef.
All three of those are in Shibuya and have some stuff you might be interested in.

When're you comin out here?