First, regarding inaccessible window header bar, one must use the alt-right click magic action to display the window manager menu and select the move window. This works wherever we click in the window. The other menu commands might also be useful. However, my opinion is that it is bad UX and inefficient.
Second, regarding NoMachine, I tested Xubuntu which doesn't depend on 3D accelerator and with some trick it can be used as an ersatz of Ubuntu. For the trick that works see here: https://answers.launchpad.net/ubuntu/+question/157817 One widget is not working, but it is not critical.
If you have 2 monitors and want to run a fullscreen video on one (using Totem or VLC) and do work on the other one.
As soon as you focus on one of the windows on your work monitors it will bring the launcher + dock to the front on both monitors obscuring the video.
One problem I have is that applications tend to change the location of their windows, especially Thunderbird. This has two nasty consequences. The first one is that the window (editing mail) might be moved to another virtual desktop when switching to another app temporarily. The second one is that the moved window may have its top bar covered by the desktop top menu. So it is not possible to grab the window and move it.
Another nasty UX is that the app menu move to the deskto top bar is sometime covered by the program name or other data and becomes inaccessible.
And finally the worst of all is that NoMachine doesn't work any more because of compiz using the 3D accelerator. The fall back to 2D is only partially working. I would like to be able to use Ubuntu desktop remotely with a secure connection through high latency and slow connections as NoMachine makes it possible. This makes me want to move away from Ubuntu.