I'm having the same problem...when i connect the plug to my 1gbit router i get non stop rebooting. When i plug it into a 100mbit switch it works fine. I tried following the guidelines at http://www.cyberciti.biz/tips/howto-linux-add-ethtool-duplex-settings-permanent.html
(except i added autoneg off) and it still wouldn't boot up when connected to the 1gbit port.
I removed the eth cable and let it boot then plugged it back in. I accessed the plug via ssh via the wireless and checked the speed of the connection for eth0 via mii-tool -v. It listed it as 100 Mbit, full duplex, link ok. But when i try to get an ip through the dhcp server on my router it fails. The green light is also still blinking on the port meaning it's still trying to use 1gbit somehow.
This is a very odd problem...