Yes, I had to do this last night, but I held it down for a while, power light didn't go off until about 5 seconds after I let go. Then when it came back up, the sound was messed up (using analog). I then unplugged it and when it came back up it was okay.
Yeah I had to do that the other night and found that unlike the DVRs you have to let go of the button before it starts the reboot process. So hold for 5 secs, let go for 5 secs. As with any computer system, a soft reset may not completely work and a hard reset may be required (unplug).
I had audio problems when I first got my 811 and called E*. The CSR told me to hold the Power button on the front panel for 12 seconds, this is the hard reset for the 811. He said the time is less for other receivers, and he gave me a summary of why it was but it has been a few weeks ago and I can't remember the reasoning behind the 12 second duration.
I've since had to do it twice, and each time I have thought about calling E* just to let them know there is so kind of issue going on. I haven't seen this problem since the 263 software, but maybe I'm lucky!