Oh for the love of God, don't you get it??? Superman is the created cliche' of a God if you go by the original comic book exaggerations. If you happen to have seen the Justice League shows lately, you'll see the toning down that Superman has undergone, simply for the fact that his original "I'm invulnerable, watch me pwn everything in the Universe" is no fun anymore. A hero can't be infallible, that was a huge mistake for DC when they first made him, and it has since been remedied. You might as well have been watching a video game where someone has put on the "God mode" cheat. What fun is anything if the hero can't be beaten? It's predictable, it gets old...FAST... and it implies that the writer has no creativity.
Anyway, like mentioned, he's powered by the Sun, and the Sun can only supply so much energy in the form of light.
Also, the stupid sneeze thing is just comic relief. Get that through your head. It doesn't even make sense, because if he sneezes in space, space is a vaccuum, and air from a sneeze wouldn't have any matter in which to produce a shockwave. Without a shockwave, that whole thing is physically impossible, unless of course *snicker* we're talking about the planets being hit by "super-boogers"
So my bad for trying to rationalize Superman, a super-cliche' character who can't be beaten and has been given no natrual limitations because the creator is an unoriginal Momma's boy. The end.