I'll start off by saying you have a very interesting product idea. Having had these issues and reading the forum posting I'm on the "still lots of spit and polish required" but I wish you the longevity to get the issues resolved.

I'm installing Untangle 5.0 on a Dell poweredge 600SC for eval purposes. Here are the issues I came across.

0) Saving changes after each input screen during "startup configuration" took quite a long time (5-7 seconds?). I realize I've only got .5G of ram and 1.8Ghz processor but really we're only writing config files!

1) First install failed while initializing swap space. It immediately shutdown so I restarted the install and it ran to completion. Not a great first few minutes but not horrible.

2) Network addessing assumed 192.168.1.x is available for the internal network. This was after I said use DHCP for the external network and it recieved a 192.168.1.x address there. I realize dynamic external addresses can be tricky (and are not likely for larger installations) but what happens when a user types 192.168.1.x as a static external IP?

As far as I can tell this could not be changed in the GUI so I edited /etc/network/interfaces manually then changed the default router and dhcp settings in the router interface which seems to have resolved the issue.

3) Now that I apparently have a working system when I try to download any of the free applications I get error dialogs that say:
"A problem occured while purchasing "{untalge-libitem-protofilter|...} "Plese try again"

Rebooting again as I'm out of ideas and haven't rebooted since cleaning up the IP conflicts.