Just bought one of these Ethernet over Power adapters. Works nicely. In fact, better than nicely. Plugged in the device that sits next to my ADSL router... connected it via the supplied network cable... Then.. find a spare power socket somewhere else in my house. Started my Mac - found the Wireless network... entered the WIFI key.. and away I am!
I went for the Devolo starter pack. Worked out at about 90GBP / 140USD. We will see how well it works at a greater distance once the office goes in (hopefully next week!)