I must say, even after only having it a day and using Hendrik's tray application (thanks again) it is surprising just how much better the USB-CEC adapter has made the HTPC experience.
My Sony TV is like Hendrik's where it does not turn off with a blank input, and only has a 1, 2, or 4 hour idle timer which is based on the last time you sent an input from the remote.
2 hours is often too short for many films, and 4 hours means there's at least an hour after you watch a film before it turns off.
Now I don't have to worry about this at all, and the TV will switch off after five minutes of the PC being idle, and never during playback.
It's also made me realize just how often the PC is left idle for more than a few minutes.
The TV seems to be a lot quicker to respond via CEC too. With CEC, it seems like it holds onto the handshaking or something, as the TV turns on with an image right away, rather than displaying a blank screen for 10-15s before the image appears if I use the remote. It just makes everything that bit more seamless.
Even if there is no further development or integration with Media Center, I think it was a worthwhile purchase.
I would of course like to see full integration to control Media Center though - but more than that, my television has a "Theater" button on the remote (many Sony TVs do) which toggles the picture mode between the current one and movie mode. This is great for switching between PC and Film use.
It would be amazing if Media Center could activate this at the start of fullscreen video playback, but I don't know if it's available via CEC. (or libCEC anyway)