I got my first series 1 used on Ebay around 2002. Since then I've had a couple Series 2s, HD, Premiere, Roamio, Roamio OTA. Even one box I paid for the lifetime subscription.
I recently bought a used Roamio basic and found it to have faulty boot issues. Since I was going to try and go OTA but found I just don't have the OTA signal to use my Roamio OTA, I decided to pull the cablecard carrier adapter from the Basic and put it into the OTA. This is done by many on the interwebs and on the TiVo forums without issue, but I experienced issues and contacted TiVo support.
Instead of trying to help me get the thing working, I was lectured about how I broke their terms of service. Funny thing is probably every TiVo I've ever owned I've modified in some way - it's sort of why people purchase them in the first place. My series 1s and 2s were upgraded with bigger hard drives and network cards, while my later ones all got larger storage. So to be lectured now about the ToS was just too much for me, so I just cancelled all my boxes. (3 active monthly subscriptions)
So let this be a warning to anyone wanting to do business with TiVo. Just don't.
P.S. Sometimes its nice to own a website that gets 2M hits/month and over 1M page views. :p