I use the 2TB WD Elements drive on my 722. No issues (Even better, I bought it from Target on Black Friday for $70). Buckets of space.
I still have three older 500 GB drives that I keep swapping on my other 622. They don't have power switches, so I just have to unplug them. I'm intrigued by the hub suggestion.... Barring the receiver automatically recognizing them (Just think of the people that will NEVER leave E* due to the video jukebox of stored content - hint hint), what's the best system to implement? Right now, I just keep swapping out USBs and plugging in the other units, but I'm afraid of corrupting data with this method of "hot-swapping".
One other complaint about the EHDs... Could you PLEASE find a way to have the list of programs go back to the point in the list where I just was? After scrolling through pages of movies and shows to something that starts with the letter "S", I notice that I clicked on the wrong episode/movie and then it goes ALL the way back to A. For some reason, it will let me do it if I click the info button BEFORE I watch any content, but if I start watching a program, it will keep going back to the beginning unless an overnight reboot occurs (reminds of the horrific bug since cured that would delete the second program you watched off of the EHD automatically - I used to keep some nothing but trailers recordings off of HDNet as kamikazes so that it didn't zap something important to me). For example, I'm watching Nikita episode 9. I finish watching it and I DON'T get the option to delete it from here at the stop screen when I'm done. So I exit to the menu, which goes back to shows beginning with A, instead of the show I was just watching...... I have to scroll back down through a bunch of screens to highlight the episode to delete. I delete it., And then I get sent all the way back AGAIN back to the top of the list, scroll down to go back and watch episode 10 (Rinse. Repeat.). It's like a programmer's sadistic game of Chutes and Ladders..... (All chutes, and then slow mind numbing ladders to get back where I was). I also keep the R Rated stuff here so my kids don't stumble on to it, so the problem is compounded by a dozen shows of the same name (Yes, I know Folders being activated would cut down on the screens, but if you DON'T enable folders, it doesn't show up in the main DVR screen which I actually like.. an easy way to segment objectionable programs away from young eyes)