I have two Xserve G5s, running Mac OS X 10.5.8 (one running Server, the other running workstation), both with multiple active local logins, using fast user switching. Each login runs Vine Server 3.1b2, set up to listen on a unique port. This allows me to have multiple “virtual user” sessions on each of the two boxes.
It’s been working great, until I upgraded my client machine to Snow Leopard. Now, using the built-in “Screen Sharing” application to access VNC sessions on either of the Xserves, most of the time I get a blank white screen. Sometimes it works perfectly. It’s very sporadic.