I know tons of people who started with a 600 sport bike.
That being said, I can't think of any of them off-hand who didn't wreck it.
I know this one guy, 300+ pounds, 6' 4", rides on 07 Ninja 250 and does just fine. He does have to wind it out and drop the clutch to lift the front up though. He's very, very hard on it. Hasn't had any problems with it either until he blew the head gasket about a month ago. It's hilarious to see to see this giant fat dude on this itty-bitty bike. Looks like a normal person on a scooter. In fact, the first time I saw him on it, I only saw it from behind and from the look (and sound) I could have sworn it WAS a scooter.
But, as big as he is, and as hard as he is on it, he has NEVER laid it down.
My R6, once you hit about 8, 9krpm (rev's to 16.5), you had damn well better have your sh!t straight and know what you're doing because things become very violent, VERY QUICKLY. It sneaks up on you too. It is such a turd at low RPM's (no torque so you use lots of throttle and VERY close gears), and it revs so quick, things happen sooooo fast. Faster than you can say "HOLY ****!" you are on the fender looking at nothing but sky.
I would never, ever, recommend a modern 600 sport bike to a first time rider. I would sooner hand them a loaded gun.
I would take a look at the Bandits. Even the new 1250's. They doing almost everything very well and make great bikes that you can grow with for a loooong time. Personally, I would suggest a Bandit 600 to any first timer. I put 10x as many miles on my Bandit 1200 than my R6 too.