[decadence]

48% of all US presidents have been Greek verified
Simply refer to list of Greek Presidents since 1900, bear in mind there were 18 before Rutherford Birchard Hayes and none were Greek then after 1900 as mentioned before three were not Greek. The total amount out of the 43 Presidents not being Greek equalling 21. Thus 49% of all US presidents have been Greek (statistic said 48% as NIC only considered their member fraternities).

123 Fraternities and Sororities source identified
Breakdown: (these are clearly international fraternities and sororities – social, single sex)
66 NIC Men's Fraternities (NorthAmerican Interfraternity Conference)
26 NPC Women's Fraternities (National Panhellenic Conference)
9 NPHC Groups (National Pan-Hellenic Council)
22 NALFO Group (National Association of Latino Fraternal Organizations)

9 Million Members Total
750,000 Undergraduate Members
12000 Chapters
Located on 800 campuses in USA and Canada

Souce "NPC/NIC Research Initiative 2000-2001".
Performed by Center for Advanced Social Research – University of Missouri Columbia.
"Representative sample of more than 2,300 students on a representative sample of U.S campuses."
Figures are from the data available to the Center for Advanced Social Research via the governing bodies.

As an FYI, Professional Fraternities not included in that figure of 123 Fraternities and Sororities have the governing body the "Professional Fraternity Association" "To be eligible for membership, a fraternity must be national or international in character and shall charter its institutional chapters only at appropriately accredited colleges, universities, or professional schools. The fraternity shall be identified by, or related to a field of study or common interest." There are 34 member fraternities under the PFA. (123+34=157).

"Most Successful Leadership Development Program for College Students" source identified
Probable origin 82% of females and 68% of males reported they joined Greek orgs for leadership training. Aforementioned 2001 study.