I've had a 1TB WD "My Book Essentials" drive active since almost the same day they raised the limit from 750GB. (In fact I had to encourage the tech who activited it to continue with the process; he was unaware of the limit increase. Always fun when vital information is exchanged in the opposite direction!) That unit has been running 24/7 ever since. I realize any drive can fail at any time. Very little on it is irretrievable however so I don't lose sleep over it.
My drive is nearly full at this point, getting down to the single digits of indicated remaining HD recording hours which began at ~100. (Of course due to excessive bit-starving/compression, those timers are very much underestimating that time for programming received from Dish, always have been. They're closer to real time for OTA stuff, but I rarely record any of that.) My stored content is a mixed bag of "keep it" and "use once - throw away". I get to the daily 1-time watch shows fairly regularly with only a few aged ones left. It's inevitable that most of us will save stuff for whatever reasons, so you too will reach the end of your capacity sooner or later!
Now if they'll just allow activation of 2TB EHDs I'll be good for another several years...!