The most common cause of lag is people game setting being to high, you can turn off all lighting and shadows and your game will improve allot (unless u have a beast machine), the game still looks great if your just playing with high detail. I play a lvl 20 wind monk that rarely misses (finness with 40 dex soon to be 42), I have all my setting at lowest except detail and draw distance... I'm playing on a computer from 2003 and I'm running the game on average at 45 fps while moving around in a public area.. in the shroud (where the lag happens allot) I don't go below 15 fps with one of thees "laggers"... I mean come on, I'm playing on a crappy dell from 03 with the only upgrades being 2 gigs of ram and a decent gfx card...

Here is a hint, allot of your in-game laggers are using laptops, you wouldn't believe the amount of people playing on laptops, and the majority aren't using machines built for games, this isn't a one way thing, to play a game you first need the hardware.