This article, from the journalism side of the Wall Street Journal, says key things were deleted from the 9/11 report by the WH:
http://online.wsj.com/article_print/0,,SB105900909639432200,00.html(subscription required)
White House Cites Security Rationale,
But Critics Suggest Political Motives
By Glenn R. Simpson and David Rogers in Washington and Scot J. Paltrow in New York
Congressional intelligence report on the Sept. 11, 2001, terror attacks to be unveiled Thursday runs to about 900 pages, but the biggest news may be what isn't found between its covers. Numerous deletions were made at the White House's insistence for ostensible intelligence reasons, several people who have seen the report said, and some of the holes raise questions about whether the secrecy sanctions were used to shield administration officials and Saudi Arabia, a longtime U.S. ally, from criticism.
...
Among the many things missing will be a full accounting of the daily intelligence briefing President Bush received the morning of Aug. 6, 2001. The White House has acknowledged Mr. Bush was told that morning of the al Qaeda terror network's interest in conducting a strike within the U.S. and that it might involve hijacked airplanes. The Pentagon and World Trade Center were attacked in just such a manner about a month later.
...
The White House refused repeated requests from the panel to turn over the president's briefing materials for that day, citing national security. A footnote in the report merely summarizes an account of the briefing that National Security Adviser Condoleezza Rice gave at a news conference last year. The gaps could fuel the already-roaring controversy over how the Bush administration uses intelligence. The White House has been shaken by revelations that presidential aides were warned by the Central Intelligence Agency not to publicize a discredited report on alleged Iraqi efforts to obtain nuclear material. In his January State of the Union address, Mr. Bush nonetheless used the report to justify invading Iraq.