Some things I've noticed:
WebAdmin seems to be fixed size in browser (Safari 2.0.4, Firefox 2.0) - why?
I've had some troubles with the initial config wizard not responding at all - after some tries I did get an "XMLHTTP Request has timed out 5 times" error. After random retries it seems to have worked, because I got a logon screen instead upon refreshing the page. I did use an ü-umlaut in the city field - is that a problem?
NTP Server didn't give a success message when adding a network and hitting Apply. Same for Email Security » Quarantine Notification.
Some Documentation in the online help on the format of the "Block These URLs/Sites:" entry in the Content filter would be handy, such as: Do I have to specify the protocol, just the hostname, or a full URL? What wildcards/regex can i use, if any?
Firefox 2.0 produces a scrollbar in the main menu on the left side which then gets partially overdrawn when mousing over the menu items - but thats probably a Firefox bug.
That's it for now, more testing next week [:)]