well, come to think of it, not alot... EXCEPT, you can always get a USB Flash Drive card (for what maybe $5.00?) and put your favorite songs on it and use that instead of buying an IPOD. the usb stick will work exactly the same way.
one of the neatest things about SYNC is that it is SOFTWARE. This means it is fully upgradable! For example version "2.0" is supposed to come out in the spring with some new features/improvements available! not to worry, if you have v1.0 you can simply download the newest version from the website to your usb flash drive and then upgrade your current version in your vehicle for free.
the future is wide open. as new cell phone technology becomes available, sync should perform the new features as well.
a couple of examples of possible future options:
Does your cell phone currently or a year or two from now offer GPS directions/navigation? If so the sync could read you those turn by turn directions even if you didn't choose the touch screen navigation option on your vehicle!
Does your teen driver's phone have GPS? you may be able to monitor their LOCATION, driving habits and/or SPEEDS! to see if they are safe, and responsible enough to borrow the car again next weekend! what parent wouldn't love to have this ability!
the possibilities are only limited by upcoming cell phone technology, which has come quite a long way in just a few years.
later,
chris