There may be one imam who is especially important to the recent Northwest Air attempted bombing, the Fort Hood shootings, and other planned attacks. He was born and educated largely in the U.S., and has lived and worked there recently.
Good news: there may be very few people who are truly a threat to attack Americans. Bad news: once again it is a relatively privileged person, with plenty of access to the benefits of Western life, who becomes radical. Are there known cases of radical Moslems becoming Westernized, to counter-balance the Westernized ones who become radical?