Apple just released iTunes 10.1, bringing AirPlay to the table. iTunes 10.1 will also be necessary to update your iPhone to iOS 4.2, whenever it's released.
So far there is no indication whether iTunes 10.1 is safe for iPhone jailbreak and unlock, so my advice to you is to stay away from it until we get confirmation from the Dev Team that it is indeed safe.
Here is the changelog of iTunes 10.1...