After an upgrade to OS X 10.5 Leopard and iTunes 8 my iPod touch stopped showing in iTunes on my MacBook. I doubt, however, that the missing iPod has anything to do with Leopard or iTunes 8 because it worked flawlessly with Leopard/iTunes 8 on my Mac mini.
I went through a lot of steps trying to reset/restore the iPod, resetting the USB adapters and so on. Although recommended in some articles I didn’t dare to uninstall/install iTunes, tough. I saved this as my last resort, for I had no desire to loose all my settings and I figured that it’d be quite difficult to get rid of all the preferences files on my system that are associated with iTunes. Turns out there’s a great article entitled “Removing ITunes for Mac OS X” at Apples’s support center.
And indeed, reinstalling iTunes 8 solved my problem.