I have the mx1 with the deskstar 1tb. In sum, in works great so far, with a few minor glitches (see below).
(1) I had it on top of an entertainment center shelf that was over a hollow enclosure. Occassionally, particularly at the beginning, I would hear a noisse that sounded like someone tapping a desk with a pencil -- the eraser end. Solution -- Moved behind entertainment center and set on a soft foam board. No noise at all now.
(2) About four or five days after install, I got the dreaded Green Screen O Death (GSOD). The problem resolved itself very quickly (30 mins) and it has worked well ever since (apprx 2 months). I read somewhere around here that this happens on a new external disk when the tivo hits a bad sector or something like that. Anyway, it works fine.
(3) Marriage of Tivo and drive took a couple of tries for me. Although, I may well have screwed up the key sequence on the remote a couple of times.
Like I said, it works great, with minimal and minor glitches at the beginning. And it is incredible have this much space on the thing. I have almost 250 tivo suggestions all the time, a ton of HD movies from HBO and the like, a couple of college basketball games I have been hanging on to, and an entire season of a couple of shows (recorded when Bravo did an all day marathon of Top Chef).
Good luck.