The Wall Street Journal has some sobering news for you and everyone else playing Farmville on the 'book: your favorite apps are transmitting your user ID to advertisers and other third parties, and there's pretty much nothing you can do about it.
And if you're into Bluetooth, the Address Book application can use the wireless technology to display the caller-ID information from a Bluetooth-ready wireless phone, provided you also have a Bluetooth device attached to your computer.