The nucleus of the comet is clearly a contact binary — two smaller (and unequally sized object) in close contact. The CNES page where this photo was released says the whole nucleus measures 4 by 3.5 kilometers, in good agreement with Hubble and Spitzer estimates. Philippe Lamy is quoted as estimating that the two components would have come into contact at a relative speed of about 3 meters per second in order to stick together in this way.
As Rosetta approached its target comet, the shape of the nucleus was revealed to be a contact binary — two unequal-sized objects in contact with each other. All together, the object is about 4 by 3.5 kilometers in size.
This unusual shape could present a navigational challenge for the Philae lander team. The CNES release quotes Philae navigator Eric Jurado as saying that “navigation around such a body should not be much more complex than around a nucleus of irregular spherical type, but landing the Philae probe [scheduled for November 11], however, could be more difficult, as this form restricts potential landing zones.”
