I am currently running 21 tuners, each kid plus my mother have their own HR24, Gene plus 3 hr24's in the theater, living room, rec room, and master bedroom.
The kids and my mothers are all isolated so nobody deletes some one else program
For me it was a two tuner DVR, had the original Tivo and upgraded to 4 two tuner Directv Tivo's. Also to get home town local channels "moved". What is keeping me is having the Chicago locals with the addition of the New York and LA big 4.
When I first picked the address I use, I was able to get both Chicago and the distants this was long before directv had HD , their was a short period of time where I lost the La HD stations (6 mo to a year) but then they came back on.