Will Ubuntu 11.04 use Gnome 3? If so, what differences for end-user is going to be? I know that there won't be Gnome shell, but what about the login screen? Will Ubuntu continue using that old (GNOME 2.X) one, or create its own, or use the new Gnome 3 login screen (maybe it will be a part of gnome shell? http://live.gnome.org/GnomeShell/Design/Whiteboards/LoginScreen)?
dv3500ea's answer was the original goal however this didn't end up happening. Sebastian Bacher posted an update to the ubuntu-desktop mailing list in January.
It turned out that it's not really possible to bring some updated components or softwares in without bringing the GNOME3 desktop (see the blueprint whiteboard for details). So the choice is on whether to switch to GNOME3 this cycle or not. The topic has been discussed several times between the Ubuntu Desktop Team members recently and we decided to stay on GNOME 2.32 for natty and ship GNOME3 in a ppa for this cycle and land it early in Ubuntu proper next cycle.
and later on:
In summary we don't feel integrating GNOME3 with a high quality level in Ubuntu is a job which can be done in one cycle and we prefer to delay it to be default next cycle.
Right now Nautilus, and the other components of the GNOME desktop are 2.32.
However you can try GNOME 3 via PPA by following the instructions in this answer: