I have a folder of mp4 videos that is sync'ed to my iPad. My question is are these videos actually also stored on my iPad such that if I delete the videos from my PC, they will still be on my iPad? Or do I have to keep the videos on my PC for as long as I want them on my iPad?
If you delete them from iTunes and sync again they will be deleted from the iPad. Sync goes from iTunes to the iPad, if you delete them in iTunes, it thinks you don't want them anymore and deletes them from the iPad. If you delete them from the iPad and not from iTunes and sync they will be put back on the iPad. It's the only way iTunes knows whether you want to keep them or delete them. If they're not checked or deleted in iTunes, they will be deleted on the next sync.