Well after typing that, I stopped by work this evening just to play around with a couple of the L lenses that we had. I'll admit, they do feel nice and solid. The control rings on these lenses also had a much smoother motion than the rings on the normal-grade lenses we sell.
But!
But, it still doesn't match the vintage lenses I'm holding in my hands right now. My statement still stands, these old metal and glass things are of a much higher build quality. Seriously, you're only going to disagree with me until you get to hold one yourself. Go find one, turn its focus ring, then come back and let me know if your opinion changes!
EDIT: I'm not saying that the L Lenses are subpar by any means, they are wonderful, solid instruments and I would be proud to shoot with one if I was a Canon user.