This link may interest you.
Hacking the Tivo FAQ
Tivo doesn't official condone the hacking that people have done to the Tivo but they have assisted some hacking efforts slightly. This probably helps them sell boxes and get new subscribers, which is their goal.
If anyone started playing with getting the subscription for free or something counter objective, they can and would put an end to this stuff.

One thing interesting to note. If you are a cable or DSS subscriber who gets channels you have not paid for, the Tivo knows which channels you are watching and when.
They could easily compare this with customer records from DirectTV or your cable company and have enough evidence to procecute you.

Just be aware is all I'm saying.