There have been several succes stories from OZZfest Bands.
Drowning Pool and Adema both went from a Third Stage Act in 2001, to a playing on the Main Stage of OZZfest 2002.
Otep graduated from Third Stage in 2001, to Second Stage in 2002. They even opened for the Main Stage several times during 2002.
Early into the 2001 tour, the crowds for Disturbed and MuDvAyNe were to large for the Second Stage and both were moved to the Main Stage. Disturbed will also play main stage in 2003.
Marilyn Manson played the Main Stage in both 1997 and 2001. Manson will also co-headline the main stage in 2003.
Slipknot made their national debut on the 1999 tour. After an incredible response to the "Crazy Clown band with 20 members", they were brought back to the Main Stage during the 2001 tour.
Chevelle (an almost unheard of band in 2002) grew such a fan base during their stint on the second stage in 2002 (and through headining their own tour, as well as opening for STONESOUR in 2003), they were offered main stage in 2003.