Well, I have done a new ubuntu 11.04 installation and also added the gnome3-team ppa and installed gnome3, which is running now.
All is perfect, except one very annoying issue:
The windows I open, have no close button at all!
This is not the usual issue that new users have when they find that the maximize and minimize buttons are gone - in my case the close button is gone too, the window bar only has the title of the window in it, nothing else.
Nevertheless I have tried adding those buttons min/max buttons to the :close entry in gconf settings (using gconf-editor or gnome-tweak-tool). There were no changes, I still have no buttons whatsoever.
Something is obviously wrong, but can't figure out what.