On the TiVO forum at avsforums.com one person reported that 2 60 Gb drives gives him almost 141 hours basic, almost 40 high quality on the standalone TiVo system.

On the DirecTiVo systems, which record at DirecTV's compression rate, there have been reports that adding an 80 Gb disk to the existing 40 Gb gives you 108 hours of record time. SO I figure 160 Gb must be around 145 or so hours...

Dave Clark
Austin, Texas
12g Blue MK2
S/N 80000329