Gagged by Patriot Act

The Hartford Courant ran an article by the director of the Portland, CT library, who received one of the national security letters seeking information. The letter carried with it a gag order, so that it took the ACLU getting involved before she could even mention the situation to anyone. While her case was high profile, many weren't:

Reportedly hundreds of thousands of security letters have been sent out. The recipients remain gagged and can never speak about their experience, under threat of a five-year prison sentence. They can never describe the scope and nature of the information they give to the FBI.

How much has been passed on regarding how many? Who knows?