If you're not a giant, you should definately consider a 600 or 750. I drive a zx6r and my buddies on bigger liter bikes cant even keep up on backroads (and they're more experienced than I). Not to mention you'll probably like the more nimble, smaller bikes being in the city. I'm biased to Kawasaki, but cant go wrong with an R6 or cbr.
Anyways, make sure all the gears shift smoothly..check for any jimmy-rigged wiring; Especially if there's any aftermarket electrics or lights. If you're getting a newer bike (such as an 07+ like you stated) chances are not much if anything will be wrong with it. Now is definately the time to buy a bike though..wait until spring and expect to pay much more for the same bike you could buy now for say $1000 less.
Also, make sure you spend the money on quality gear. A nice helmet (Shoei, Arai) will make riding much more pleasurable; Not to mention a shitty helmet will discourage you from actually wearing it. But I wont turn this into a gear thread, just dont take your skin for granted.
Alright I'm done rambling, welcome to the 2 wheel world-