I missed it, but apparently TiVo released Home Media Engine, an open development kit (SDK) for making applications that run on your TiVo.

There are two parts, the HME itself, and the Bananas UI toolkit for making TiVo-like interfaces.

The HME protocol enables third parties to write applications that display on the TiVo box.

This is more than likely a response to the growing number of MythTV users and enthusiasts. By providing a turn-key hardware setup and solution with near-immediate and assumed SAF (Spousal/Significant-other Approval Factor) it also allows hackers (the good kind) and enthusiasts to satisfy their desire to customize and modify.

An enterprising Indigo user is already developing a TiVo app to control his home automation.