I've managed to install elementary desktop by rebuilding ubuntu-extras-keyring locally on my system, like this:
mkdir somedir; cd somedir
sudo apt-get install -y debhelper
wget http://archive.ubuntu.com/ubuntu/pool/main/u/ubuntu-extras-keyring/ubuntu-extras-keyring_2010.09.27.{tar.gz,dsc}
tar -xf *.tar.gz
cd ubuntu-extras-keyring-2010.09.17
debuild -i -us -uc -b
sudo dpkg -i ../ubuntu-extras-keyring_2010.09.27_all.deb
After that, elementary-desktop will install, but will error out at the end because it depends on systemd-shim which is no longer needed nor wanted with 15.04 having a full SystemD implementation.
When it errors out, run
sudo dpkg --force-depends -r indicator-datetime
sudo apt-get purge unity-control-center unity-control-center-signon
and it should complete the installation.
I expect in the near future the Elementary folks will fix their repository to handle SystemD properly - Ubuntu 15.04 move to SystemD was done a few weeks before the official release and the Elementary guys probably didn't have time to adapt to that.
After installation, you can log out and see "Pantheon" in your display manager's session list, but if you try to log in you'd get just the blueprint paper styled Elementary "beta wallpaper". The problem is that the session starts Slingshot and Gala, but not WingPanel or Plank. Currently I'm using using Slingshot's ALT-F2 shortcut to open the launcher and run Plank and WingPanel manually (just type the name in all lowercase and hit ENTER).
Best Answer
Sure, I'm running it right now, and it's working pretty well mostly. There are two major problems that I'm experiencing that are deal breakers for me. Both problems affect only applications that are not eOS applications, such as firefox. When you start one of these applications, and right click on the icon in the dock, and click "keep in dock", it doesn't work. The bigger problem is that the titlebars for non eOS applications are completely broken. The close button does not work, nor does the minimize or maximize button.
Here's what I did to install it:
You can then download the source for elementary-tweaks and compile it locally.
If you use
make install, the.soinstalls in the wrong place. By default, it installs in/usr/local/lib/switchboard. You'll want to move it to/usr/lib/x86_64-linux-gnu/switchboard.After that, elementary-tweaks works quite well.