Yeah, the cursor line in the spinner is quite choppy, indeed. But not as in the replay mode, that ones are squares!
Currently, my revision 6 Leapmotion unit runs on my USB 2.0 (I don't have 3.0) at 100 fps or at 150 fps in hi-speed mode. But I played osu with leapmotion on limited 60 fps - I've had performance problems when on unlimited and even at 120 fps.
The problem here is that I need 3 applications for running Leap: LeapApp (basic leap application, eats ~25% on my Core2Duo, ~10% on my notebook i5), my mouse emulator and osu!. These three applications try to outrun each other and run as fast as possible. Osu! eats most performance of them when in Unlimited mode, so there is less processor time for other two apps to update cursor position. It can be tweaked by process priorities a little.
Solution would be having Leapmotion code implemented right in osu!, it would need much less performence and input lag would be even lower. It's unnoticable for me even like this - I once turned on vsync by mistake, that was some input lag! If I analyze my video frame-by-frame, there is some small noticable lag... Again, it's much bigger because there is one extra application on the chain.
If there was some way to tell osu "mouse" coordinates at exact time there are needed, there would not be any problem like this - osu! would tell my application "hey, I need mouse coordinates right now" and wait until my application didn't get them for it.
Anyways, even this dumbed down version is more than enough for my osu level - I have bigger problems using my keyboard than leap
(I never tried it before). Aaaand this is only temporary solution. I will try to get around it somehow, and there will very probably be some better mouse emulator in the final release.
Oh, and latency is about 7-8 ms when using one finger and ~15 ms when using both hands.