These days, many games come with some kind of level system. Hitting good shots, having kill streaks and simular stuff gets you points that after some time make your player level raise. I think this is one of the main reasons for people to play games like Call Of Duty. Even in casual play there is some kind of competition involved because everyone wants to be better than their friends.
However, I think this might be what QuakeLive needs to attract more players. I imagined it like this: Things like hitting an impressive or earning an excellent medal give you let's say +50 points. Your score is displayed on your profile so you can compare with other players. This system could even be extended if id added propper medals for airrockets, airnades, holy shit and maybe even for stuff like long shots. The scoring system should obviously not add weapon upgrades and other gameplay gimmicks - it's only purpose would be encouraging new players to stay dedicated to Quake Live.
It could even be used to fight some of the game's deficits. If quitting mid match would cost you 100 points maybe the number of quitters reduced.

This topic was brought up before on the QL forum:
http://www.quakelive.com/forum/showthread.php...#post26040

Discuss.