Wireless Syncing has been activated with the release of the 2nd beta of iOS 5 and iTunes 10.5.
In iOS 5.0 beta 2, wireless syncing is now available for the Mac. It requires iTunes 10.5 beta 2 and 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.
Wireless syncing is triggered automatically when the device is connected to power and on the same network as the paired computer. Or, you can manually trigger a sync from iTunes or from Settings - General - iTunes Sync (same network as paired computer required). Be sure your device is plugged into a power source when performing Wireless syncs.
If you find issues with apps, media and/or photos synced to your device, you can reset then resync. From Settings -General - Reset, choose Erase all Content and Settings. Then reconnect to iTunes and sync again.