I tried again: Installing 20100324-0246, upgrading to 20100324-2048 from console.
Following the steps of the original post.
After activating the bridge and setting LAN to "none", I get:
netstat -rn
Destination Gateway Flags Refs Use Netif Expire
default 87.52.xx.1 UGS 0 15 vr0
87.52.xx.0/24 link#1 U 0 708 vr0
87.52.xx.120 link#1 UHS 0 0 lo0
127.0.0.1 link#12 UH 0 1127 lo0
127.0.0.2 127.0.0.1 UHS 0 0 lo0
192.168.yy.254 link#13 UHS 0 0 lo0
(plus a lot of IPv6; xx and yy are my sanitizing).
Link#1 is the LAN, #12 is lo0 and #13 is the bridge.
After reboot I get:
Destination Gateway Flags Refs Use Netif Expire
default 87.52.xx.1 UGS 0 47 vr0
87.52.xx.0/24 link#1 U 0 137 vr0
87.52.xx.120 link#1 UHS 0 0 lo0
127.0.0.1 link#12 UH 0 19 lo0
127.0.0.2 127.0.0.1 UHS 0 0 lo0
192.168.yy.0/24 link#13 U 0 1 bridge
192.168.yy.254 link#13 UHS 0 0 lo0
But this time, I get no working GUI even after reboot :o