Quote Originally Posted by Celestia View Post
Superman's flight is an extension of his ability to leap tall buildings and is, therefore, based on superstrength, not gravity immunity. Also, in All-Star Superman, his weapon vault contains a "gravity gun" that he explicitly says can hurt him. He later uses that very same gun on Lex Luthor after Luthor acquires all of Superman's powers. Thus, Superman is most definitely not immune to gravity manipulation.
Superman was given flight as a logical extension of his original ability to leap tall buildings... But they are not the same ability. While he isn't immune to gravity, he's obviously capable of exerting force on his body without using his physical strength. IIRC, it's explained as some sort of limited telekinesis. At one point, he even mentions at that things seem lighter when he's flying.