Mine seems fine, but I mostly use the ViP622. I've had good luck with avoiding most 721 bugs over the years, but I'm on my 6th 721 due to HD & power supply failures.
I hate to even think about it, but its not as buggy as the 522 right now. It was bugging out real bad but I have not seen the 721 do that for a little while now.
I'm not sure what software I have but I like my 721 and it seems to work fine. After the Dish 1000 install I had problems with it loosing all the channels on the 119 satellite even though it got signal but a reboot fixxed it and I haven't seen it again since. Thats the only problem I've really had with it.
I doubt they will want to give us NBR on the 501/508/510/721 due to the fact that they are not getting the $5.99 monthly DVR fees on those receivers so they have no incentive on adding that function on those. They will want people to migrate to the 522/625/622 receivers so that they will want to pay that $5.99 DVR fee to get the NBR function as well. I think it really helps with the recordings particularly when you have certain actors that you like. To some it may be worth it. The $5.99 fee almost cancels out the $5 additional outlet fee that is waived if the phone line is plugged in.