I've put this detail in a series of posts, but it really deserves a full post. According to the May 30, 2005 Bradbury memo, Khalid Sheikh Mohammed was waterboarded 183 times in March 2003 and Abu Zubaydah was waterboarded 83 times in August 2002.
On page 37 of the OLC memo, in a passage discussing the differences between SERE techniques and the torture used with detainees, the memo explains:
The CIA used the waterboard "at least 83 times during August 2002" in the interrogation of Zubaydah. IG Report at 90, and 183 times during March 2003 in the interrogation of KSM, see id. at 91.
Note, the information comes from the CIA IG report which, in the case of Abu Zubaydah, is based on having viewed the torture tapes as well as other materials. So this is presumably a number that was once backed up by video evidence.
The same OLC memo passage explains how the CIA might manage to waterboard these men so many times in one month each (though even with these chilling numbers, the CIA's math doesn't add up).
...where authorized, it may be used for two "sessions" per day of up to two hours. During a session, water may be applied up to six times for ten seconds or longer (but never more than 40 seconds). In a 24-hour period, a detainee may be subjected to up to twelve minutes of water appliaction. See id. at 42.  Additionally, the waterboard may be used on as many as five days during a 30-day approval period.
So: two two-hour sessions a day, with six applications of the waterboard each = 12 applications in a day. Though to get up to the permitted 12 minutes of waterboarding in a day (with each use of the waterboard limited to 40 seconds), you'd need 18 applications in a day.  Assuming you use the larger 18 applications in one 24-hour period, and do 18 applications on five days within a month, you've waterboarded 90 times--still just half of what they did to KSM.
The CIA wants you to believe waterboarding is effective. Yet somehow, it took them 183 applications of the waterboard in a one month period to get what they claimed was cooperation out of KSM. 
That doesn't sound very effective to me. 
Sign the petition telling Attorney General Eric Holder to appoint a special prosecutor to investigate torture here.
Update: Here's one reason to demand a special prosecutor to investigate these actions. In addition to revealing the sheer number of times KSM and Abu Zubaydah were waterboarded, the memos reveal that the interrogators who waterboarded these men went far beyond even the expansive  guidelines for torture described in the Bybee Memo, notably by dumping water onto their nose and mouth, rather than dribbing it on.
The IG Report noted that in some cases the waterboard was used with far greater frequency than initially indicated, see IG Report at 5, 44, 46, 103-04, and also that it was used in a different manner. See id. at 37 ("[T]he waterboard technique  ... was different from the technique described in the DoJ opinion and used in the SERE training. The difference was the manner in which the detainee's breathing was obstructed. At the SERE school and in the DoJ opinion, the subject's airflow is disrupted by the firm application of a damp cloth over the air passages; the interrogator applies a small amount of water to the cloth in a controlled manner. By contrast, the Agency Interrogator ...  applied large volumes of water to a cloth that covered the detainee's mouth and nose. One of the psychologists/interrogators acknowledged that the Agency's use of the technique is different from that used in SERE training because it is "for real--and is more poignant and convincing.") [my emphasis]
There's been a lot of discussion about whether those who did what the OLC memos authorized should be prosecuted. But in the case of those who waterboarded KSM and Abu Zubaydah, that's irrelevant, because they did things the OLC memos didn't authorize.