have to disagree with you there. the fixed drivetrain carries your foot through the "dead spot" or the point at which your legs have the least amount of leverage on the pedals.

personal experience has shown that if i train exclusively on a fixed gear for a long period of time, my pedal stroke gets lazy at that point and i have to work on my form when i get back on the road bike. especially on climbs.

training fixed is great for other things though, like keeping my heart rate up and developing power at high cadences. singlespeeds can be great for these too.

mixing it up is what works best for me.

edit: too slow