I am regularly doing the LLOD support over phone+remote console to the production support guys. Our software runs on virtualized headless Fedora 5 instances that are accessible solely by ssh, as it should naturally be.
It turns out to be a waste of time to the person on the other end, as he just listens to me explaining what I do, without really seeing what goes on.
So, I decided to use GNU screen to share the console between us.
I log in as a user and start screen on the command line. Then, I enter ^A:multiuser on[RET]. That is, I type Ctrl-a, then I type a : to enter the screen's build-in command line. I can now activate the multiuser mode by typing multiuser on in the screen's command line that appears in reverse color at the bottom of the console window. To execute, I hit Return.
The other guy just has to log in with the same user and type screen -x to connect to my screen session running in multiuser mode.