So far I have tried: checking the appropriate boxes in "Desktop Sharing," and then trying to log in using my email address from "Remote Login" at the login prompt on a different machine. It doesn't seem to work, however. Clicking the question mark next to "Remote Login" says that I need an Ubuntu Remote Login account, but then clicking "Set up" makes the screen go black for a second, then returns me to the login screen.
One thing its Desktop Sharing, and another very different is Remote Login.
In Ubuntu you have Desktop Sharing while using a program and service called vnc server this program needs to be installed either with synaptic or with the ubuntu app market.
Once this application is installed you can share your Desktop and someone can connect to it from the local network in the current session.
A Remote Login can be done installing a SSH Server, then from a remote terminal type :
$ ssh -Y username@remote ip address
It will ask if you want to add the ssh key type (YES) then type the remote user password and then once logged in just type startx
This will initiate the default window manager (unity or gnome).
Or from a linux desktop login choose REMOTE LOGIN then type the local IP of the machine that you need to use.
You may also initiate a separate session using VNC but the basic idea of VNC its to share the current live session instead of initiate a new one.
A basic difference between SSH and VNC is that VNC does compress the video and images streamed to the client while SSH does not, but the image quality its very good
Other advantages of VNC Clients is that they can be installed and executed in almost any device or OS, Google Chrome itself have one extension, Windows, MacOS X, iOS, and Android as well.
But in my own experience its easier and quicker to install TEAMVIEWER, it does work flawless in ubuntu and any other OS, and you can access your desktop from anywhere not only your local network, the only cons is that it can't open a separate session as SSH X or VNC.