TiVoPony tells us that TTG and MRV will come to the Series3 and TiVoHD units in November, via a software update.
There will be some restrictions, as always, but by and large, you’ll be able to move content between any combination of HD and SD unit that supports these features. You won’t be able to move HD to an SD box (sounds like it won’t down-rez) and you won’t be able to move copy protected content at all. But it does sound like HD content will be movable to a computer – pretty cool!