Yapadapaduuuuuuuu! While biking i became enlightened. Just disabled the network and it boots (VirtualBox 4.2.16, OS X). It seems the system hangs around trying to get some IP address via DHCP?? I don't know why it does so long (minutes) and requires such a lot of CPU time (though of the VM) doing so, ... but it's working just fine! Just some more years 'till i know what i'm talking about!!
--steffen
