Update 1: iOS 5 Final version has been released for Download and Jailbreak - Click Here
New amazing feature has been ported for the first time to iOS-based devices via iOS 5 beta 4. Apple has just announced that iOS 5's WiFi-sync functionality is now available with Windows PCs starting from iOS 5 beta 4.
In iOS 5 beta 4, wireless syncing is now available on Windows as well as the Mac (requires OS X 10.6.8 or Lion)You will see an option to enable wireless syncing when you connect your device to iTunes with the USB cable. It is recommended you perform your initial sync with a cable after restoring your device.”[via]