Just noting this for future reference, but I finally got iTunes working properly on a Windows PC that would at random:
– transfer some songs to iPod Touch devices successfully,
– transfer some other songs, then crash, then the device reports no music on it, or
– corrupt the device so badly it needed fresh firmware restored.
And the the culprit turned out to be…. Zone Alarm. No kidding. Turn off Zone Alarm and everything worked instantly.
iTunes is still a god-awful PoS though, but at least it’ll now transfer music and apps. If you’re getting “app could not be installed because it is not signed” issues with iTunes, and you’re installing legit apps, chances are that turning off Zone Alarm will fix it right up. Amazing.