When you replace the Premiere's drive with another then use the original on another Tivo (or even use it on a PC), you will not have a backup if/when the new drive fails, or if you need to warranty return.
Original S1 (Recycle Heaven)
Series 2 (PLS, sold)
TiVo HD (XL, PLS, "652")
Juliet Basic (4XL, PLS)
The TiVo Apocalypse begins on Sat 2013 Feb 16 00:00 GMT!