yes, I did have to hack the firmware to load my own software, but that's not a major thing even for non-experts to do nowdays (look at 'rooted' or 'jailbroken' phones, there are a lot of them out there, and a lot of them are not owned by computer experts)
or what it's worth, I agree with Ingo and Linus, that availablility of the code is what matters. If Tivo is doing something special in their kernel, what's most important is the ability to see what they did and decide if it's something that benefits other users (and if so modify the upstream kernel). I can get/build other hardware to run the software on. If a particular vendor chooses to lock down their hardware, it is up to me to decide if I want to support that vendor by buying their hardware, or buy their competitors hardware instead.
In the phone world we are seeing this happen. Initially the vendors all went in the direction of locking things down, but now a growing number of them are being pressured to not lock down the bootloader. This isn't because of the license of the software, but because there are enough vocal users that they are getting the message.
forbidding locking down hardware will limit a lot of 'good' uses as well as a lot of 'bad' uses, and I don't see it as being worth it.