My guacamole server then connects to x11vnc so I still get RDP-like performance across the internet.
Edit: you'll also want to make an Upstart job for x11vnc so that it starts on boot, and restarts if (when) it dies. You can just copy any of the basic upstart jobs in /etc/init.d/*.conf and investigate. You also may want to make x11vnc start after your X server: http://upstart.ubuntu.com/cookbook/#run-a-job-before-another...
There is a lot of fiddly business :/
Very much still a compile-it-yourself experience. When I was setting up my RDP server on my Mint media center, I went with xrdp + x11rdp setup detailed in some guides at ScaryGliders.net, although the same guy as released a bunch of scripts to do it for you, see https://github.com/scarygliders/X11RDP-o-Matic
I don't really want to deal with recompiling stuff and manual updates though, and expect others to feel the same, which is why I advocated x11vnc to the GP.