Environment iMac OSX 10.7.5, iTunes 10.7, iPad2 with 6.0.1 and iPhone 4S also with 6.0.1.
I sync only with USB.
Last night, for the first time, I turned on Home Sharing so that I could "stream" a movie to my iPad to watch it. After doing that, plugging in either the iPad or the iPhone did not "connect" the device to iTunes. The device did connect to the computer, as evidenced by iPhoto starting up and displaying the pictures on the item.
Turning off Home Sharing did not help, until I restarted iTunes (with Sharing off), at which point, plugging in either device does the sync that I expect.
So are Sharing and USB Sync (or sync in general) mutually exclusive somehow? How is the sync/sharing interaction supposed to work?