The Onion used to have this article, "Fvck everything, we're doing 5 blades." I think Gillette may have forced them to take it down since I can't find it anymore.
I've used the Mach 3 turbo for a couple years now and it has been pretty nice. My girlfriend bought the Quattro a couple weeks ago and I tried it out. It seems to make me press it harder into my face since it doesn't pivot at the same point as the Mach 3. The fulcrum is directly above the cartride on the Quattro while it is behind the cartridge on the Mach 3, so there is less direct pressure.
The Quattro has the trademark "safety wires" across the blades that I thought would affect shave quality and closeness, but you really don't notice they're there. I managed to get a very close shave with the Quattro without any irritation. I usually get a bit with the Mach 3 on my neck. It was a pretty nice shave overall. I was especially surprised that my girlfriend told me the blade was about 2 weeks old!
My only beef with the Quattro was that it becomes clogged with hair and skin cells that cannot be rinsed away. My girlfriend didn't have this problem as the razor was spotless when she handed it to me. I'm not sure how this would impact long term performance, but if it's only cosmetic, I'll probably switch.
I still have another 2 months supply worth of Mach 3 razors and the powered Mach 3 is coming out in the next few months, so I may wait before taking the plunge on a new razor.