yea, i noticed right off the bat with my rev jr. that the sweep knob is the key to getting the sound you want out of that thing...it's amazing how much you can alter the entire voicing of the amp with that shit
i'm too lazy to make/upload a vid, but it works by changing the frequencies of the lo/mid/hi controls of the EQ section. at first i thought it was just some sort of sweepable midrange boost...but then i actually read the manual, and learned that it changes the frequency of the other knobs. this, of course, gives shitloads of tonal options, and i constantly find myself changing the settings on the sweep knob depending what guitar/pickups/tuning i'm using.
and metaltastic...the VHT's might not make it onto a lot of albums, but i've seen them used live by both suicidal tendencies and isis, and i can tell you that they sound fucking great