Depth perception - The threat of an upset is always hanging over the heads of the top seeds. Who will play Cinderella in this year's expanded field of 68? Can Pitt, perhaps the most vulnerable No. 1 in the field, survive the opening weekend? As the mid-majors gain ground, the margin of error has narrowed.
Upsets at top include: 2006: No. 11 George Mason d. No. 1 UConn, 2008: No. 10 Davidson d. No. 2 Georgetown, 2010: No. 10 Saint Mary's d. No. 2 Villanova and No. 9 Northern Iowa d. No. 1 Kansas.