Having driven two rentals with Sync, it's the most annoying thing I've encountered in a car so far. It didn't sync with anything Bluetooth: iPhone, GPS, or earpiece, and its "help" requires reading the manual before use to be of any value, so "on the fly" is a non-starter. Intuitive it's not.
If I were to buy a car with it already installed, I'd demand a discount. Great idea, woefully inadequate execution.