Background firmware updates via the network?

Are there any official or unofficial Atmega Arduino variants that have an onboard programmer so that software updates can be downloaded as a low priority background task and then applied on the next reboot without having to be connected to an external programmer or AVRDude running on a PC?

I've seen the Freetronics ethernet update method, but it requires a live connection (like AVRDude) and is complex to setup.

Mike