Windows Phone 7.8 builds just popped up on the infamous Navifirm app that scans Nokia's software servers. The builds are available for at least the Lumia 800, 900, 710 and 610. These are not production builds, they are Nokia Care builds which means they are intended to be used at Nokia Care service points. That could mean these very close to the final builds that will be made available in January.
Those of you who haven't flashed a custom ROM so far, I recommend you wait a couple more weeks to the official update. The rest of the geeks can go download Nokia Care Suite and install it like you would any custom ROM.
Image courtesy of GSMArena.