I'm having the same problem. WiFi Sync seems like such a great idea, but it's way too restrictive. You have to have the Mac turned on, with iTunes running; you have to plug the phone into a power source; it seems that it only checks once a day. This morning, I wasn't even able to sync manually, even though iTunes was running. I had to uncheck "Sync with WiFi" in iTunes for my phone, then plug the phone in to the Mac so iTunes could see it, check "Sync with WiFi" again, and then a manual sync worked.
But I have still been completely unsuccessful with automated sync.
iCloud's Photo Stream works perfectly. I want iTunes sync to work like that (with the obvious difference being that iTunes has to be running on my local network.)
I just got mine working! I too could manually Sync over WiFi, but no automatic syncing even after 8hrs on the charger, for either my iPhone 4 or iPad.
On a few sites they recommend checking iTunes Preferences -> Devices and ensure that
"Prevent iPods, iPhones and iPads from syncing automatically" was unchecked -
Which mine was.
I had also uchecked/checked the "Sync with this iXxxx over WiFi" was enabled - no luck for days.
Finally I noticed a consistent item on screenshots of those who claimed it was working:
The "Open iTunes when this iXxxx is connected" option was checked - since I have my iTunes set to start when the iMac does mine was unchecked.
I enabled that for both, rebooted everything and it worked like a champ.
To validate I disabled the "Open..." item on my iPad and left it enabled for my iPhone 4 - the iPhone still syncs on WiFi when I put it in my desktop dock (that is only plugged into the AC/USB power supply) but the iPad does not. I re-enabled it for the iPad, re-docked and the sync started immediately.
I'm running a Windows 7 Ultimate with iTunes 10.5, iPhone 3GS with iOS 5.
iPhone will not sync over Wi-Fi and is not even seen in iTunes unless plugged into laptop.
Sync with wi-fi box is checked on summary page.
Open iTunes when this device is connected box is checked
Prevent autosync is not checked
under Device Preferences >Devices >Prevent iPods, iPhones.... is unchecked.
On iPhone iTunes Wi-Fi Sync remains greyed until connected directly to laptop via USB