And thanks a lot! It surely helped me!!!
Finally I am able to use the nvidia driver in X, without having to do a dirty shutdown afterwards, becuse of the system hangup I got when trying to logout or switch to a virtual console.
Actually I now know two ways to avoid the situation.
1. Unplug the video cable before booting the computer. This way the TV-out will never be started , and there is no problem to leave X. (With the cable plugged in I get a cloned monitor picture on the TV, which goes away when I start X.)
2. Install and run nvtv and push the "TV Off"-button as you explained.
I hope the NVIDIA folks will fix this soon. Until then I think they should put a note in the installation materials for the nvidia driver stating that the nvidia driver can not be used with an active TV-out port, or the system will hang when it switches from X graphics back to normal graphics again.