My friend who works at the NSF offices told me that they have a random number generator. At the press of a button, it generates a random integer between 1 and 250. Starting April 1st at 9am, they press the button on the hour, twenty-four hours per day. They release the results if and only if the number 195 comes up. (195 because the NSF was founded in 1950.)
To calm email-checking neuroticism, people have reminded us that the emails were sent out in the dead of night last year. Indeed this is true. However, in 2008, the emails went out at 1:00pm on Wednesday, April 2nd. (This is true; I keep good records.) So really they can potentially come at ANY TIME. Better check away AHHH!!!!