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.
Series 2 (Retired, sold)
TiVo HD 1TB (157 HD Hrs, PLS, "S3HD")
Roamio, Oh Roamio!
The TiVo Apocalypse begins on Sat 2013 Feb 16 00:00 GMT!