Apple's latest version of the FireWire Development Kit includes an app called AVCVideoCap.app which will capture video at a specified time from a FireWire-connected HDTV-tuner. Not only will it record, but it will also change channels too. (You cannot, however, schedule a variety of shows to record in sequence, only one at a time)
Download the latest Firewire development kit here. Install the FireWireSDK21.pkg package and go to the /Developer -> FireWireSDK21 -> Applications folder and look for AVCVideoCap.app.
Captured files will be approximately 100Mb/min. depending upon the resolution of the HD video and the compression settings used.
To play back the resulting files, either:
Use MPEG StreamClip to edit, then save files as MPEG, then playback with QuickTime Pro (using the MPEG-2 playback component. Alternatively, use VLC and play the file directly without further modification.
[kirkmc adds: I haven't tested this.]

