I recently moved and ever since setting up my desktop, I've had seemingly random losses of my wired connection, although high bandwidth stuff (Netflix, maximizing an HD YouTube video) seems to trigger it fairly reliably.
I'm fairly certain it's something to do with Lubuntu. After the last outage, I hooked up a laptop to the same port on the router with the same cable and it connected just fine. My wireless phone and tablet also maintain their Internet connection.
Rebooting temporarily fixes the issue. Sometimes I need to reboot twice.
What do you need from me to diagnose? :)