I've been lucky enough to attend a few of these parties. I have been to a few other lan parties as well, and while there is something to be said for bringing your own computer, having all the computers with all the games preinstalled definitely makes it a more frictionless experience. From "let's play something" to playing it is typically about five minutes (except GTA, but that's probably because it's old enough to still offer IPX networking as an option).
