Why would ssh-agent still be running even after the ssh session has been terminated?

I noticed ssh-agent processes being owned by various users who have at one time ssh'd into my workstation.

Session isn't being ended properly?

Chris

ssh-agent is the daemon that gives the key to the *ssh clients*. It has nothing to do on the server.
It is usually started when you login locally in your X environment and then it exports to its subshells (all in this case) some environment variable to be reached by X clients.
So, in normal case, it should be started once and when you logoff, it should be stopped.

In your case, that's strange that ssh-agent is started for incoming ssh connections..
Then probably connected to your ssh server and then started (manually) ssh-agent to connect to another ssh server from yours. When they logoff, depending on the process Parent PID, these processes can stay yes.