I'm running iTunes 11 on my Mac with an old iPod touch (iOS 5) serving as a jukebox and an iPhone 4 (iOS 6.1) as my main device. Both are set up for wireless synching.
When I start iTunes, it finds the iPod and synchs with it wirelessly without trouble, but it doesn't find the iPhone, forcing me to connect it to synch with the dock cable.
If I disable wireless synching for the iPhone in iTunes, synch, re-enable wireless synching and synch again, wireless synching returns and works again.
Until such time as I quit iTunes and restart it.
Why does this keep happening? It can't be a network/firewall problem, because the iPod keeps on synching with the same machine through the same network. Needless to say I'm finding this pretty frustrating, what's the point of wireless synch if you keep having to re-enable it with the dock cable every time you start iTunes?