Sometimes it’s practical for the same person to setup multiple accounts on one machine for distinct purposes. While the fast user switching feature in OS X does make it easy to quickly move between accounts some people may find it more practical to be able to interact with the desktop of a different account while still logged into another one. If you’re this kind of person then you may find this post useful.
The method I’m using, which is based on information that I found in some forums, involves using Screen Sharing to connect to a different account on the same machine.
All of the necessary features are already built into OS X but unfortunately they won’t work in this scenario (by default). If one enables Screen Sharing, and then attempts to use the Screen Sharing app to connect to the local host, the screen sharing app will not connect and instead state that it cannot connect to the same computer. I’m not certain why this check is actually needed but it turns out that the check for enforcing this is not sophisticated.
It appears to only be checking for a connection to the local machine on port 5900 so changing the service to use a different port will work.