Is it true that in a manual transmission vehicle, if the engine RPM is right, you can shift gears (up and down) without pressing the clutch? I've heard a true truckdriver never has to touch his clutch pedal (until he's coming to/fro a stop) :)?

Some will, not sure if all will. I can with my S10 but dont think my saturn will.

Yes you can. I have done this a lot in the past both shifting up and down. If you let off the accelerator just enough that there is no strain on your tranny, you can pop it into neutral. Once it is in neutral, get the engine rpm's up or down to what you think they would be for whatever gear you are trying to shift into, and once the shaft is spinning the right speed, it will allow the gears to mesh and shift.

yep, sure can, uncle trucked for a good 10 years and never touched the clutch except from dead stop and into double od, and its possible to do in a car, get the timeing just right and you can slam first to second, second to third is the hardest but possible to do, its called speed shifting