This is not a great solution (slow, expensive, and clunky) but if you have (or are considering moving to) DirecTV and their DVR you should check out the Nomad. You move shows to it, and it moves them to the iPad or iPhone.
My best guess is that there is some bit-rate lowering (read: secondary compression) done for portability (the programs on a DirecTV DVR are MPEG-4 AVC at about 7.5 GB per hour) which is why it is not all that fast, but I think the quality is at NetFlix level once on the iPad. Since it includes a hardware transcoder it should be faster than doing that in software. In iOS 6, new iPads (maybe even iPad 2's ?) can AirPlay out.