BZFlag

For the uninitiated:

BzFlag is the best linux multiplayer game available. Up to 10 people are supposedly supported, but personally I've only played with 6. You have a tank, you move around a square, and kill other tanks (preferably of the other team - killing your team-mate results in your own death) with the help of superflags such as laser, machine gun, shockwave, thief, high speed, etc. And tanks can jump (but unless you have wings, you can't maneouvre in the air, which is frustrating as you jump and then have to wait to fall down right in front of someone who's about to shoot you).
There are buildings, and little transportation gates, and you can have bad flags too. You have a radar screen and a heads up display.
Basically - masses of fun. Team play is the best - especially if you have the genocide flag - then kill one person and their whole team dies! so exciting.

Definitely the best hons procrastination technique I've found this year. Come on Paul, you know you want to play!!!!

Ok. Must start writing seminar :)