I think jamz nailed it. When it comes to glass, Zeiss, Leica, Nikon, Schneider, and other glass-makers are pretty much on par.
But the Leica cameras are so quiet that you can photograph someone without him/her even knowing it. Not a big deal if you do studio portraits, but a definite plus if you're aspiring to be the next Cartier-Bresson and you're trying to get those moments-frozen-in-time shots.
Nonetheless, I think that gadget hounds--whether it's cameras, stereo equipment, guns, cars, motorcycles or computer buffs--tend to be braggarts more often than necessary.
I spent the last few days shooting a job in a rental studio with their equipment. In this case, the camera was a Sinar-P 4x5. All of the micrometer hashmarks and two gazillion adjustment knobs look really impressive...until you need to get to work.
There's something to be said for simplicity, whether you're a Marine ready to fire on an Iraqi insurgent, or just a plain photographer wanting to get the beer shot when the head of foam is perfect.