To everyone complaining about performance and lag issues please realize this.
The demo has been out for less than half a day, no one knows what settings to tune to properly optimize the game and get it running smoothly, give it a couple days.
As for lag, of course there is going to be lag right away! There are hardly any dedicated servers up for the game and those that are up are most likely being spammed to hell. Like the performance issues give it time! In one week everything will be resolved and you play to your hearts content.
For now just load up the single player or play a game with a few friends to try it out. In a couple of days log on to some servers and see how the game really plays.