You can backup all or individual Steam games to DVD, or HD. It creates a single .exe to reinstall all or individual backups. I keep a backup of all my games so I never have to re-download them. We can also use them to setup a bunch of machines for a lan party. Steam has stated as previously posted that they would issue a run without connection patch if it were ever necessary...
Steam is the gratest distribution / buddy system to date. It keeps all your games updated for you, allows you to chat and organize games with your friends. I cannot see a single drawback to it. And I am old, if anyone should be an old crotchety tin-foil hat wearing, black helicopter seeing, NWO fearing chicken-little, it should be me.... but I love it....