It surely has been short-lived. The Planet Offer mode in Cities XL is closing down, as of March 8, 2010. This is the MMO mode of the city-building game from Monte Cristo, and the appointed reason is a know one: not enough people playing.

The game will be solo only from then on, and Monte Cristo is already working on Cities XL 2011, an improved version. They also say there is a "manual and risky process to import Planet Offer cities into your Solo mode" that will be revealed soon.