Think I have eleven left.

Oh, I just saw you had 1000... I guess there are more for the DLC?

The EXP/Skill on Halo 3 is just for bragging rights. And there's an achievement (two actually) for reaching 50 in any playlist. And I guess you get the "psycological warfare" benefit for it: When someone sees they're playing against a level 50, they might cower in fear and just let you kill them.

Also, it's used in matchmaking to put you into groups with people of similar 'experience' in the game. Trying to make the playing ground as equal as possible.

I like in BioShock2 that they give you new masks and hats and stuff when you reach the higher levels and they also unlock audio diaries. But you get access to better weapons and plasmids too, so in that way it's uneven like COD/MOD. But, then again, you still get EXP points just for playing a match, so everyone can level up, it's just slower if you suck.