A user on the Tivocommunity forums discovered an undocumented feature in the latest release of TiVo Desktop for the Mac (1.9.3). If you add a line of code in the OS X Terminal program, you can get videos on your Mac to show up on your Now Playing list on your networked TiVo. Cool! Details of how to do it in the discussion topic linked above.
[Via PVRBlog]