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."
Something that happens when someone is being beaten by double their score or more. Originated in Modern Warfare 2: Free-For-All. The person that did this is now allowed to brag about it and make fun of the person and the other guy can't say anything because everyone knows he sucks at the game.
Joe: "Dude! I totally uber-pwned this one guy!"
Ben: "Really? What was the score?"
Joe: "I got 1500 and the other guy got 750."
Ben: "Dude I just got uber-pwned. The guy got 1500 and I only got 400."
Joe: "Wow you must really suck."