getting absolutely destroyed in some kind of competition or event, usually in a videogame like Halo. pwn is derived from "own" but the o is replaced with a p, whiched is supposed to represent a tongue sticking out, therefore forming the word "pwn". I pwn noobs all day. but back to the uber part, uber is a synonym for "super", but it usually has a negative connotation.
"Daniel pwns Dylon in Halo, but its all fun and games".
"Dude, you just got uber pwned."