One common issue is not being able to change the port it runs on (default is 5900) ... simply put, I have not seen a true way to do this within the client itself. I wanted to move to a non-standard port (partly for security by obscurity, though I realize that's not real security). Other folks have the issue of wanting to connect to multiple Macs inside the same network.
A real hack that came to mind is this: I have an Airport Extreme router (though almost any router should suffice). From outside the local network, you can configure the router to port forward, as shown in this Apple article.
Use the Port Mapping Setup Assistant to map the following:
Port 5906 on the outside (Public) can be mapped to (Private) port 5900 on machine 10.0.1.2. Hit Continue, then add additional mappings as needed, ie:
- Port 5904 on the outside (Public) can be mapped to (Private) port 5900 on machine 10.0.1.3
- Port 3283 doesn't seem needed for ARD VNC access.
- Etc.
- VNC to port 5904 to get to Mac #1 running ARD Client in dual screen mode.
- VNC to port 5906 to get to Mac #2 running ARD Client.
- VNC to port 5908 to get to Mac #1 running normal VNC client. I'm still running 10.4.11; as far as I know there is no way to get ARD to reduce its color depth under 10.4 as you can under 10.5 as shown in this hint. So it's painfully slow to do dual screen, full color depth, but occasionally it's needed when I need to get to something on the 2nd monitor.

