Editing in Quicktime works perfectly - indeed instantaneously compared to EyeTV.
Steps: download and run cTivo -- thank you Thrillcat!
Download a show from the TiVo using "Decrypted TiVo Show" to be the video format.
Open in Quicktime. It plays fine. To edit, choose "Trim" from the Edit menu -- a slider appears, select what you want to keep, press the "Trim" button, and viola -- done. You just need to save the resulting new video and delete the old one if you wish.
To edit out commercials, "Split Clip" at start and again at the end of the commercials, select just the commercials, then "delete" from the Edit menu. Done. You just need to save the resulting new video and delete the old one if you wish.
Quicktime version 10.3 (latest), OS X Mavericks (latest). I thought it might be because I have the infamous $20 Quicktime MPEG-2 component installed, but I just tried it on a Mac where I'm pretty damn sure I didn't install it, and it worked fine there as well. Try it for yourself guys.
I still haven't figured out how to get Quicktime to pass the 5.1 sound onto the optical digital sound out - Quicktime movie inspector shows the sound to be 5.1 AC3 (5.1 sound does obviously work on my Mac via EyeTV, Apple DVD Player and VLC -- I have never tried before with Quicktime though) - tips welcome.
Totally off topic, you can stop reading here (but I need to vent):
TWC wasted a week of my time, including 5 hours today until they finally got my TiVo CableCard working because someone in their central office hadn't bothered to authorize any channels on my account. The cable guy who was at my house today suspected that was the problem from the beginning (as did I), but it took him and his supervisor hours and hours on the phone before they could convince someone to fix it, while in the meantime they were forced to prove the negative - that nothing else was broken, over and over. Just pathetic. The guys who TWC sent here were great, but the rest of the company, the less said the better.