I checked WikiPedia and got this:
Cloverfield is the working title for a 2008 film being produced by J.J. Abrams and Bryan Burk, written by Drew Goddard and directed by Matt Reeves. The film is scheduled to be released by Paramount Pictures on January 18th, 2008. The premise is a giant alien known as "The Parasite" invades Earth and it is filmed entirely with handheld cameras. Also known is that the movie isn't even done filming and the trailer was filmed before the movie was finished. Not much is known about the movie, and it has been widely regarded as a secret movie and Cloverfield may be a temporary working title.
A teaser trailer was shown prior to the screening of Transformers. The trailer consisted of raw camera footage. During the trailer, a group of friends in their 20-30s are throwing a party in New York City for "Rob" who is moving. They feel vibrations and assume that it is an earthquake and quickly evacuate to the rooftop. Once there, they see explosions and debris flying in downtown Manhattan, and a terrifying roar echos in the streets. You can hear a voice shout "It's alive! It's huge!". The final scene features another terrifying roar and an object careening into buildings and crashing near to the camera operator in the street. When the object comes to rest, we can see that it is something that resembles the head of the Statue of Liberty. The title of the film was not shown during the trailer.
It is rumored by some to be a secret Godzilla movie, due to the setting in New York and the references to Japan in the teaser video (the Rob character is moving to Japan the day after the teaser is set). Some have mistaken the title for 'Best Night Ever' because of the last three words in the trailer, spoken by someone holding a camera aswell.
Looks like we'll have to wait and see. There's also a website up for the movie, but there's nothing on it yet but a single frame from a video camera. See the second link for it.