Maybe it's because I get 100% of my information about Microsoft from Slashdot, but one of the points that surprised me from Thomas Hawk's interview with Media Center bloggers was that plenty of Media Center people have TiVos too.
Charlie Owen: Also by the way, You might be surprised to hear me say this, but if you try and like a TiVo, buy a TiVo. If, on the other hand you want something with more power, flexibility, adaptability and upgradeability choose a Media Center PC.
However, and a big however, I don't believe this is a entirely a Media Center vs. TiVo choice -- I know lots of people with both in their homes, peacefully coexisting (including eHome team members). I believe the market is big enough for both to thrive.
That point is illustrated perfectly with EtiVo by Shahar Prish (via Matt Goyer). It's a program that takes video files off of a hacked Series 1 TiVo and turns them into WMV files. While it isn't a MCE app, it seems like it could be integrated pretty easily. You can already control EtiVo from a web interface or a WinCE PDA.
Maybe some enterprising hacker will build an MCE front-end to TiVoToGo for people with MCE and Series 2? Heck, while we're lazywebbing, how about a TiVoToGo interface for Xbox Media Center?