Several friends and clients have lost automatic syncing in recent iTunes updates on the Mac. It even happened to me.
Somehow, the updates to iTunes 10.4 misconfigure iTunes Helper, which is behind-the-scenes software that, well, helps iTunes weave its magic.
Here’s how to fix it on Snow Leopard. This fix may or may not work in Lion, too.
Plug in your device and open iTunes. On your device’s Info page, uncheck “Launch iTunes when this iPhone/iPad/iPod is connected.”
Unplug your device and restart the Mac. Launch iTunes, then connect the device. Put a check back in the box next to “Launch iTunes when this iPhone/iPad/iPod is connected.” If this is solving your problem, iTunes should ask if you want to install iTunes Helper. You do.
That should do it for you.
Growing up, my favourite book was “Arty the Smarty”. It was about a small, wiseass fish who outsmarts everyone. I wonder what I saw in that. You can read its acid-browned pages for free online. My copy looks exactly the same.