Hmm, boy I don't know if I buy into the shifting without using the clutch thing. I have heard about guys racing MX not using the clutch but that is racing. The things people do during a race is for one thing, to win, not for the benefit of long term, trouble free operation out of their machine.
I have used the clutch to both up and downshift since 1985 and have never had to replace a clutch or had a tranny go out on me. I don't race dirt bikes but I am just as fast as the people I ride with so it is not worth it to me to not use the clutch.
On a related topic, when I was in college my Automotives instructor had over 100,000 miles on his Ford Ranger and said he never used the clutch except to start off. His reasoning was that each time you engage/disengage the clutch you wear it out just a little bit. Eventully it becomes worn out from normal operation. But if you shift without it, then there is no wear. Of couse you have to be good enough to shift the tranny when engine RPM and transmission RPM is synchronized, then it goes in and out of gear no problem. I believe the older big rig trucks were like this. The problem is finding that sweet spot each and every time to shift when everything is in sync. Way easier said than done.
During one of my summer jobs, my buddy and I infilcting some serious wear on a 5 yr old Ford F-350 transmission by trying to master the art of shifting without the clutch. By the end of the summer the synchros in the transmission were so worn out it would hardly go into 1st gear even with the clutch and grinded going into the rest of the gears while using the clutch. Without the clutch is was a very forced effort to shift the truck.
From my experience, I have found that the clutch is there for a reason so you might as well use it. Another thing to consider is that it is far less expensive to replace a clutch than rebuild a transmission.