The back cover of next week's Amateur Photographer magazine reportedly has a full page teaser ad by Olympus about their upcoming camera. The campaign slogan is "Oh My Goodness" indicating than their product announcement may be related to the old Olympus OM system. The text says something like "the latest Olympus classic in a long line of design masterpieces".
Update: On January 3, 2012 Olympus registered the trademark Olympus OM-D wich will probably be the name of the new camera:
The German Patent Office also has a registration for the "OM-D" logo:
Olympus definitely likes teaser, as you can see from previous announcements: