I must say, Turnkey linux is amazing. For someone who wants to be on top of things server-wise, learning linux is key, and well, having access to software that works the first time around helps a whole let and makes troubleshooting a little less of a headache.
And to help you with with "future" appliances , I offer these three suggestions.
1) File server/print server. I am a bit surprised that it wasn't done already, since Ubuntu server edition actually offers samba as an option. But with the turnkey concept, it would make it even more user-friendly. Also, perhaps even throw in Icecast and make it into a media server?
2) Webcam server. Although Linux and webcams aren't exactly in love with each other, this could be a nice alternative to some commercial network cams who have the unfortunate habit of been hackable (in the bad way) I.E. www.metacafe.com/watch/327094/google_hacking_how_to_watch_and_control_webcams_videotutorial/ . So to have that in linux could make it perhaps more secure and scalable?
3)Primary Domain controller. Although it could be done with Ubuntu server edition, it would be nice to be able to set up an entire domain with just a live CD in case of an emergency. Just a few clicks and done.
Thanks and keep up the good work!!