I had the same problem. Here was the solution I found. Connect your iPad to your Mac via cable, just like before. When iTunes starts and recognizes your device, open your iPad in iTunes (Devices), scroll down Summary to Options and click Sync over WiFi. It should work like a champ. That one step - having to enable wifi sync in iTunes - has not been documented anywhere I have found.
Here is how it work on both my iphone 4S and Ipad 2.
OSX 10.7 updated, Ipad Update to ISO 5; Iphone 4S on IOS 5
Itunes must be running. Plug in Iphone or Ipad it works the same.
1. Under Devices slect iphone or ipad
2. Under Summary tab; options check on Sync with this Ipad; iphone over wifi.
3. Click apply on the bottom right.
4. Click Sync on the bottom right.
now you are ready to sync wirelessly with out being connected to power. You do have to do
it manually but the following works as long as the devices are on. I have tested with them with
what I call asleep. It does work.
If you are in Itunes on your computer you can select the device you wish to sync and then click on
sync in the bottom right hand corner. It will begin to syn and show it on either device.
In my testing both devices and my Imac are on the same wireless network.
Next; On your iphone or ipad got to settings
Once you have synced you are now set to sync wirelessly. I am not sure yet what gets synced.
I am still testing that.
On your device go to settings/general/Itunes Wi-Fi Sync, select Sync now. In a second or two your device should show that it is syncing right next to the wifi signal indicator.
I have doing it this way for two days.
Let me know if I have missed a step or something.
Hope this helps someone.