It seems there are some serious issues with Beta 4 and the Fon+/Fon 2. The problem occurs with unmodified OpenWrt 8.09 RC1 as well so it's not just an issue with the Gargoyle additions. If you are using Gargoyle on one of these routers, stick with Beta 3 for now.
While I tested thoroughly on the classic La Fonera, I only got my Fon 2.0 the day before release. Since Kamikaze 8.09 supposedly works on this router, I only did a cursory check to make sure Gargoyle installed properly -- definitely a mistake!!! Someone has already submitted a ticket to the OpenWrt developers, and I will see if I can figure out what is going on as well. Interestingly, the symptoms I can replicate on a Fon2 aren't as severe as reported in the ticket. I can boot the router without problem (which is why I didn't initially catch the issue), but it crashes if I try to restart the network.
I will post here again when this is resolved. I am very, very sorry for any inconvenience this issue may have caused anyone.