Most LANs I've seen run with one box with an HDD on it and the others are disc only. Cheaper and less items to track to prevent something from walking out the door.
With Halo 3: Mythic, you didn't even need a HDD on any of the boxes. The benefit to having an HDD on the host box was saving films and playing premade gametypes. For Reach this was using post-ship gametypes. With 1.1 in play, you''re going to need to decide if you want to play just Vanilla Reach or buy an HDD for each box, give them their own gamertag, and you still have to buy Defiant and Noble separately for each box since they're not going to be available via disc for the forseeable future.
As I said in my HBO post, worrying about the LAN community isn't going to resonate very well with constantly online-connected people, and I'll admit that. The interesting thing here is going to see how MLG reacts to this. They're the ones that are financially affected by this the most on a considerable scale.