Welcome to the site and to GT ownership!
The major difference between the '06 and '07 model is the brakes. My '06 GT has servo-assisted brakes. The '07s don't have the servo, and are made by Continental-Teves. Most people like them or will
like them better, as they have more of a traditional (linear) feel to them. I personally LOVE my power-assisted brakes.
On that '07 of yours, you will be able to install the ASC option this coming Spring. ASC is traction control. Another option that I could give 2 hoots about...but many are excited about it.
RDC (tire pressure monitoring system) is also available as an option. I believe that this option is available to both '06 and '07 models. You may already have this on your GT.
And lastly, a Xenon (HID) headlight upgrade will soon be available for all new GT owners. I'm going to go the aftermarket route, saving myself $400-$500 in the process. Stay tuned to this forum for more thread regarding HID upgrades.
As for the shaft, just ride it like ya stole it!
I have owned several shaft bikes in the past that behaved much differently than a chain-driven bike. But these new Beemers don't suffer the ill-effects of a shaft due to their awesome suspension systems. Just be careful rolling on the throttle coming out of a curve. The rear tire will break loose on ya. I'm used to this as I've owned several powerful bikes. But this may surprise and/or scare the bajeezus outta someone that's not used to that.
Keep the questions rolling in, and welcome again!