From MtGox's facebook page:
https://www.facebook.com/MtGox/posts/468895216528224Statement Regarding Dwolla:
Like many who have contacted us, MtGox has read on the Internet that the United States Department of Homeland Security had a court order and/or warrant issued from the United States District Court in Maryland which it served upon the Dwolla mobile payment service with respect to accounts used for trading with MtGox. We take this information seriously. However, as of this time we have not been provided with a copy of the court order and/or warrant, and do not know its scope and/or the reasons for its issuance. MtGox is investigating and will provide further reports when additional information becomes known.