FoneArena have posted the above demo of the Windows Phone 7.8 ROM which can now be downloaded from Navifirm for the Nokia Lumia 800 and 510.
The ROM does have the new start screen, accent colours, the ability to select Google as your search provider, and most interesting the new Bing wallpapers.
The demo unfortunately shows that the ROM only contains the Microsoft bits, without the Nokia bits like Bluetooth file transfer and the Ringtone maker. It is possible Nokia will distribute these via the Nokia Collection later.
The presence of the ROM on Navifirm suggests a more general roll-out can not be too far in the future.
Thanks Code for the tip.