Update: The White House has now posted the presidential memo (.pdf) explaining the new order and directing the Attorney General (when his appointment is finally confirmed) to issue new guidelines "reaffirming the commitment to accountability and transparency". Here's a highlight:
The Freedom of Information Act should be administered with a clear presumption: In the face of doubt, openness prevails. The Government should not keep information confidential merely because public officials might be embarrassed by disclosure, because errors and failures might be revealed, or because of speculative or abstract fears. Nondisclosure should never be based on an effort to protect the personal interests of Government officials at the expense of those they are supposed to serve. In responding to requests under the FOIA, executive branch agencies should act promptly and in a spirit of cooperation, recognizing that such agencies are servants of the public.