Good one Elgordo. Let me take a crack at it with the little knowledge I have.
Slew Rate: how fast an amplifier can swing it's voltage, measured in Volts / millisecond or something like that. I think amps with "higher" slew rates sound more analytical.
Damping Factor: determined by the amplifier's output impedence, may relate to their ability to "control" a speaker. I think amps with higher Damping have tighter bass.
Negative Feedback: some of the amp's output is "fed" back to the input, but in reverse phase. The effect being that it forms a self-controlling loop. If the amp's output goes too high, more of it comes back to CUT the input, thereby bringing the output back down.
I hope that made sense, and I hope that is somewhat accurate - no engineer here. Now, the REAL question is, do any of these really say anything about the SOUND of the amplifier? I personally don't think so. I think great numbers are easily acheivable by any manufacturer, but not all high-end amp makers even care about the numbers. Personally, I like tube amps, which often have reasonable SlewRates, poor DampingFactor, and NO negative feedback. Go figure.