Normally when I play fullscreen games in Linux it is really annoying, since they tend to display in the middle of the displayable area: that is, half of the game on one monitor, and the other half of the game on the other monitor. It's slightly annoying, although I just disable one of my monitors when I go into a fullscreen game.
However I discovered today with Sauerbraten that it seems to map itself across the entire viewable area. So I end up having the game spread fully across both monitors. It's actually pretty sweet, and if you have dual head and Linux set up, I suggest you try it out.