I've run into a really odd problem that I previously thought was a duff router, but turns out to be linked to when Ubuntu doesn't shutdown properly.

Occasionally I've had Ubuntu stall whilst shutting down (although I've yet to dig into why), and had to forcibly power off my PC. For some reason, this kills all the wired connections on my router (Linksys WRT56G version 7). I can still connect to it wirelessly and access the configuration page, but all wired connections (including the connection to the modem) are down. No amount of power cycling seems to fix this, but everything starts working again once I boot Ubuntu.