Update 2: According to the fine folks over on NeoGAF the motherboard in question is nothing more than the Clarkdale PC processor that combines a dual-core Nehalem derivative with Intel integrated graphics. Saying, "It has absolutely fuck all to do with the 360".
Update 1: "Microsoft does not comment on rumour or speculation."
Original Story: Kotaku has shots of a motherboard for what is claimed to be for an Xbox 360 Slim.
The board also shows the CPU and GPU chips combined into one wholesome chip, with testing recently held and completed in China.
It's also rumoured it's part of a bigger plan to see a Slimmer 360 out at retail.
We'll email Microsoft, but don't go expecting anything massive, innit.