[MikeCStig]

Are we bringing this topic back out for its 10th anniversary? Ok, what the hell it's an interesting topic that I know a thing or two about.
There are 2 types of transmissions mentioned in this discussion (or argument maybe) synchronized (like in cars and light to medium duty trucks) and non synchronized (like in heavy duty and commercial trucks). The answer to the question "should I float gears?" is different for each type.

Synchronized transmissions- my answer would be probably not. The sychromesh gears in this type of transmission were meant to work together with the clutch to make shifts smoother and easier. No need to double clutch, gears can be changed at any RPM using the clutch with a single press. It's actually now more difficult to shift without the clutch and not damage the transmission. It takes a gentle touch most people don't really have, and if you botch too many shifts, it will grind the synchros and tear the transmission apart as it fills up with loose metal shavings. Just use the clutch, it's not that hard.

Non-synchronized transmissions- totally different. With no synchromesh, things get a little tricky. I've driven a couple of semi trucks (not far since I've never had a CDL, but I've done it) and the shifting techniques involve more than just pushing the clutch one time and going to the next gear. First, you have to wait for the right RPM corresponding to your throttle position (and no there is no shift light), then push in the clutch once, go to neutral, release the clutch, push it back in and go in to the next gear... all timed just right so you catch the next gear at the right RPM.
The alternative to this is of course, floating gears. With a non synchronized gearbox, a perfectly safe option, and much easier than the double clutching madness described above. You can basically feel every thing through the shifter. When it seems like it's about time to shift, start to come of the throttle and the shifter will start to loosen up. Pull it out of gear, lift off the throttle and ease it into the next gear (don't force it, or it will grind if you do), all done without even touching the clutch. What makes this method preferable is the number of gears, and the fact that if you do use the clutch, you have to double clutch.
One of the trucks I drove had an eaton-fuller 9 speed manual and that was the lowest number of gears I encountered. It was pretty smooth once I got the hang of it. The other one I actually drove was a Rockwell 10 speed that didn't like to cooperate until it warmed up, which for me it never did, since I only did short trips, but even so, all that clutching will take a toll on the left leg. Even worse, there are such things as 12,13, and even 18 speed transmissions. That's why most real career truckers stop using the clutch soon after passing their licence tests, otherwise their left legs would fall off.

So in conclusion, unless you're driving a commercial truck, use the damn clutch, it's easier than trying to float through the synchros.