I figured I'd post this in case it could be helpful to anyone. I was having problems with my HR10-250 that had a factory WD 250GB drive and a Maxtor QuickView 300GB drive I had bought pre-formatted from Weaknees. The unit was one of the original units shipped, so going on 2 years old, and it was starting to reboot randomly, stuttering during playback, and I could hear the hard drive clicking. I opened it up and it definitely sounded like the clicking was coming from the A drive (which I suspected anyway since it was about 6 months older). It still had enough life in it that I was able to finish the few shows that I had only on that unit, so it was never really "dead."
So I purchased a new unformatted Quickview 250GB drive from weaknees. I was worried I might have problems backing it up since the hard drive was failing, but it seemed to work fine while doing the backup, and also when I restored it (after I remembered to put the drives on separate IDE channels!) and then added the second drive. But after less than 1/2 hour it started rebooting again, and it would get stuck on the Welcome screen when it rebooted (unless I unplugged it myself). So I tried restoring the image to the drives individually - the 300GB drive that's a little over a year old and the brand new 250GB drive both had the same results - started up fine initially, but had problems within 20-30 minutes. So I was starting to wonder if the hard drives weren't the problem after all. Then I tried it with just the original WD drive that I had suspected all along, and it wouldn't even get past the Welcome screen.
Since that bolstered my suspicion that it was a bad drive as I had suspected all along, I thought maybe the image I had made was corrupt after all, and I tried it with the image from my other HR10-250, which I knew was good. I had hoped to avoid that since I knew I'd have to clear & delete everything, but I had little choice at that point. Anyway, it worked - at least for 8 hours or so before I went to bed last night. I also made a backup image of this unit after it did all the clear and delete and guided setup stuff.