The Do Not Fly list gets longer every day. It’s apparently at nearly 1 million names.
— Yes that’s 1,000,000 names. — Including the 14 of the 19 9/11 hijackers who happen to be dead.

The reason for the use of the word “apparently” is because the list is classified. Even congress has trouble seeing it.

The ACLU maintains a counter and information here.
The DOJ has a report here that includes the following:

Failure to Modify and Remove Watchlist Records
According to HSPD-6, each nominating agency involved in the
watchlist process is responsible for, on an ongoing basis, providing terrorist information in its possession, custody, or control, thus ensuring watchlist
information is current, accurate, and complete. Additionally, nominating
agencies should generally provide information to remove an individual from the watchlist when it is determined that no nexus to terrorism exists.
During the course of an investigation, the FBI may acquire additional
identifying information on watchlisted subjects. FBI policy includes
requirements for updating and removing watchlist records of investigative
subjects and states that it is “essential” that this additional information be
used to enrich an existing record. To accomplish watchlist record revisions,
the FBI uses the same process for initially nominating an investigative
subject to the terrorist watchlist.
However, several FBI personnel informed us that the modification of
watchlist records is not being performed on a regular basis. NCTC personnel
also stated that they see very few modification requests from the FBI.
Moreover, many of the FBI employees with whom we spoke were not aware
of the standards for determining when a modification of the watchlist record
is necessary. As a result, certain watchlist records are likely missing useful
information.

60 Minutes ran this story.
(This segment was originally broadcast on Oct. 8, 2006. It was updated on June 7, 2007. )

Just a few oddities from the ACLU site:

U.S. Senator Edward Kennedy (D, Mass.) After repeated delays at airport security, the senator had trouble getting removed from the airline watch list despite calls to Homeland Security and eventually a personal conversation with the Secretary of DHS.

Marine Staff Sgt. Daniel Brown was blocked from flying while on his way home from an 8-month deployment in Iraq. He was listed as a suspected terrorist due to a previous incident in which gunpowder was detected on his boots, most likely a residue of a previous tour in Iraq.

Major General Vernon Lewis (Ret.); a recipient of the Army’s highest medal for service, the Distinguished Service Medal who served in the Korean and Vietnam wars, Lewis had problems flying.

And my personal favorite:

Sister Glenn Anne McPhee, the U.S. Conference of Catholic Bishops’ secretary for education. Sister McPhee sought redress and removal from the watch list for nine months in 2004 and 2005 and it wasn’t until she was able to elicit help from White House connections (Karl Rove) that DHS addressed her problem.

As soon as I heard they had started a new organization called the Department of Homeland Security, I thought heard the sound of jackboots and Wagner.
I was right.
If you have faith in the DHS read the Patriot Act closely and remember that everything in it applies to you, not just some other guy. You should also go to this site.