I'd updated my Macbook to Mountain Lion, everything works fine. In fact, iPod Touch 4th generation is also visible in iTunes but iPod touch 3rd generation is not appearing in iTunes. Please find below use case:
When I connect iPod touch (3rd gen)
a) It starts charging, and the Apple logo appears, but is not visible in iTunes in Mountain Lion.
b) It starts charging, and the Apple logo appears, but is visible in iTunes in Snow Leopard.