I just bought a '96 CBR600 F2 with about 20k to get my start in the sportbike world, and it's not too hot to handle at all. Right now I'm just working on getting the feel of riding around in normal situations, but I'm still not comfortable enough to take it out during rush hour. For other newbs unsure whether to get a 250-500 or a 600cc, I'm gonna say take an older 600. I got mine for $2400 (which may have been a little steep???) so I'm not worried about what might happen if I drop it in a parking lot or some similar situation, like I would have been with a newer 600. Also, this bike definitely has enough power for me right now. Anyway, I'd say it's all about comfort; ride something you're not afraid of!
Oh, and I took the MSF course last fall, it really helped. I'm glad I waited to buy my first bike after dropping those Blasts a couple times while doing parking lot maneuvers... I don't think I would have been able to handle a 600cc first without that class.