I just heard about this on the news, but don't know much about it. It's gotta be freezing cold in that river. I heard it's something like an A320 or that size. It was flight 1549 on its way to Charlotte, NC and only managed to get up to 3200 feet before crashing.
One of the theories is that a flock of large birds might have contributed to this crash, but it is not certain. This theory was based on a witness account. The pilot also reported two bird strikes to controllers. It's possible that the crew had readied the passengers for a water crash.
*Update* All 151 passengers and crew have been taken off the plane and are OK. Witnesses say they could see them being rescued from the top of the plane before it sank.