Quattro and Others:
I've tried the Mach 3, the Quattro, and that five-bladed thing from Schick, and I came to the same conclusion with all three - their blades are too close together to rinse clean under today's water-miser faucet aerators. If you don't rinse the cartridge really clean, the soap and skin oils left between the blades shorten their life, due to tiny amounts of corrosion that you can't see. However, due to the extra-fine tolerances of a razor blade's edge, it is enough to notice while shaving. It takes a pretty forceful blast of hot water to knock everything out of the eensy-teensy spaces between the blades, and today's faucets just can't deliver that.
It's not that the cartridges don't do what they're supposed to do. When you break out a fresh one, they're fine. But I find that they get significantly dull in about five days, due to the problem I've described. Blame it on the need to conserve water. And at the price of genuine Gillette or Schick cartridges, five days is an unacceptable lifespan, IMHO.