A word of warning for anyone using the Delay TV function (ie pause and rewind) when viewing the HD channel. I guess cos the amount of data for the HD transmissions are around four times as much as a regular standard definition one, the buffer used for Delay TV seems to fill up after around twenty minutes. I was using it for the Michael Palin broadcast last night and it came out of pause after about 20 minutes and I couldn't re-pause it. When I then started watching again, the box did a complete reboot after half an hour's viewing. I was recording an SD channel at the same time, but I would have thought the box could cope. It couldn't.
I've seen posts on the Sky HD forums that suggest a similar issue on Sky boxes, especially if recording two HD channels simultaneously (we should be so lucky!) - I think it would be fair to say that the current generation of HD PVRs are very much 'first generation' and there's a limit to their capabilities at the moment.