I bought an R1 as my first bike this past Friday for my 21st birthday.
I have been on several 600's before this and they never impressed me and, like several others have said, didn't make me respect the bike. The bike I learned on was a stunt-caged 98 (I believe) 636 with a 15 over sprocket. The 636 never impressed me one bit, as it's speed was all in the gearing.
The R1 forces and commands respect with it's pure power and torque. A lot of reviews I read before purchasing the bike claimed the power band as the weak point. Personally, I find it to be a strength, as you're not in full power from a take-off. I feel like it makes the bike a little easier to ride around town at lower RPM's.
However, when you do grab a fistfull of throttle, it demands the respect of the rider and screams "HANG ON!". To be honest, I bought far more bike than I need, and it actually scares the shit out of me every time I ride it--for now, that's a good thing.
Anyway, I probably wouldn't personally recommend learning on the R1, as I'm doing it now, and it's not easy. I learned how to ride on the aforementioned 636, but this bike has a whole new learning curve!