NP. One thing rumored to be coming down the line is Multi Room Viewing, they've mentioned a whole home solution on a number of financial conf calls. What this would allow is for viewing of something recorded on one HD DVR on another HD DVR over your in home ethernet network. I see you have three 722's according to your sig, if you got three HR21's like you have on the 722's you'd be able to record two things on each and then watch the recording on any of the HR21's.
No, there is no time frame on when this would be available and it hasn't been demo'ed. But at last months CES show D* did show a PC runing a client that showed content from a HR2X DVR, so since they're working on the server part in the HR2X series maybe it's not too far away, we can hope.