This is precisely a 12.04 HDMI output problem, because it works for 11.10 - everything else are the same, only the OS version is different.
The symptom is that on my HDMI output TV screen, it always shows Unsupported resolution even after setting it to the resolution that works on Ubuntu 11.10 (via gnome-control-center, in which it detects my TV just fine), I still don't see any output on TV.
The audio is not working either.
I think it is 12.04's problem, because if I boot into Ubuntu 11.10, and everything else remain the same, HDMI output (video & audio) work just fine.
12.04 is a freshly installed, just the vanilla Ubuntu HD installation.
How should I nailed down / fix the problem?