I haven't used many racquet technologies, myself, but my coach back in college raved about his PK Kinetic, and swore that it cured his aging, aching elbow. I gave it a few swings, and I remember it being pretty comfortable (and shaking it like a maraca). I'd actually love to try one again.
I thought Wilson's PWS (perimeter weighting system) was a sound idea. That extra bit of material in the hoop mimicked having a little lead at the 3 & 9 positions. I thought their Aire Shell handle system, which was supposed to reduce shock, may have worked a little too well, because the Pro Staff that I had that used it had a distinct lack of feel.
I had a lot of fun playing with a Prince Extender RipStick for a while, but it didn't necessarily improve my game. Serves and slices felt effortless (and wicked) with a 29" racquet, but depth and directional control on groundstrokes was more challenging due to the length and sub-10oz weight. Switching back to 27" 12oz racquets felt immensely better.