I had been wondering why media sync and iTunes sync stopped working. I have WebOS 1.2.1. I had been installing various homebrew apps and Preware. I also updated iTunes to 9.0.1.8. At first I thought that I should downgrade back to an older version of iTunes which had been suggested in other threads. It didn't work with 9.0.0.7 or 8.2.0. My Pre would briefly show up as a removable drive on my PC while in media sync mode and then the drive would disappear. Of course, iTunes then would not "see" it as an iPod either. Then someone brought up the possibility of homebrew apps interfering with the sync process.

It turns out that myTether which I recently installed was interfering with media sync and therefore iTunes syncing! Having the WiFi and USB Tethering off is NOT enough. You also have to have USBNet off in the options menu of myTether (which requires a reset of the Pre when you change it) for media sync to be re-enabled. My guess is that USB Ethernet Gadget (network adapter) function must have priority over the iPod function. Is this correct?

What a relief to finally get at the cause of the problem. Now everything is working again on my Pre. Loving the Pre.