I've never used a TiVo either but here's why I like BTV better.
When you build an HTPC and stick it in your living room along with all your other stuff, you get a lot more than just a TV recording system. For instance, I now have several thousand mp3s available in my living room anytime I want. I also have a nice internet radio selection. I don't pay for Sirus radio but I get a few stations for free through Winamp. I can get instant updates, RSS feeds, etc. It turns out that having a full PC in your living room rocks.
I live in Houston, one of the best OTA HD cities in the US. I have 3 HD tuners and 2 analog tuners and I can easily record with all of them simultaneously while I play the aforementioned mp3s or watch something else that I've already recorded. I can also watch TV in my office using BTVLink which is kind cool since I also have a few security cams wired into the antenna system. And if I'm really a TV junkie I can burn shows to DVDs to save forever.
And the best ever... once I got everything to work, I got almost immediate "wife acceptance" for the HTPC. I really think having all our music instantly organized and available is what sold her but why complain?