I remember in ubuntu jaunty I tried to use ubuntu net-book remix. it worked and it looked so great, but I had no way to return to Gnome Desktop.
then I decided to remove ubuntu net-book remix but the title-bar disappear on maximized windows.
will it happen on unity?
If I correctly understood an old question I did, yes you will be able to do it. Just like now you're able to select NBR or Gnome session when you login, with Ubuntu 11.04 you'll be able to select a Gnome session at login. The only difference is that Unity will be selected by default.