One note to people who ordered the Limited Edition, in many of the limited edition copies when it's been opened it looks like the first disc has come loose from the spindle and may have gotten scratches from being loose in the package, there's many reports of people from Wal-Mart or Gamestop checking Limited Editions where they can hear the disc loose inside, and in the video from 1up where they opened their stuff that microsoft sent them the disc fell out of the Limited Edition. This isn't an issue for standard or legendary since they have different cases, but if you've preordered the Limited Edition you can check your copy when you pick it up and see if somethings shaking inside it and if you feel really concerned that the disc is damaged you can ask for them to give you one that's not loose. Although people are saying that the discs usually still work and it might not even be the game disc but the bonus disc.
And the lining up for Halo 3 is stupid, if you have a preorder you'll get the game anyway and if not then you're sure to be able to get the standard edition (maybe the limited edition and most stores aren't getting any Legendary editions beyond their preorders).