I'm still relatively new to street bikes, so this is new to me. A couple friends that used to race say they never clutch on upshifts when they're racing or getting on it, only on down shifts, which makes sense.
My bike has been apart since they told me this so I haven't had a chance to try it. They say to just roll off the throttle about 50% and pop the next gear, and then back to WOT.
I clutch 95% of the time and have on occasion not used the clutch on hard upshifting and easy downshifting. I can't say I really notice an advantage to not clutching during a shift, then again I don't spend any time on the track.