The "Official Xbox Magazine" says in the October issue that 8,000 Microsoft employees are participating in the Halo 2 beta, 14% of the entire company. That's an amazing number!
What does this mean for general Microsoft productivity right after November 9 when Halo 2 ships? Well I think there will be a lot of late nights spent with employees fighting the Covenant, and not a lot else. There will be some employees who will wait the few weeks for the discounted version to show up in the company store, but there will also be the super-keen who will be lined up outside local stores at midnight to get their full-price copies as soon as they can.
Xbox Live is disabled on the corporate network, but assuming it works like the original Halo, System Link games will work between conference rooms so long as they are on the same subnet. As many of the conference rooms sport nice big projectors, I predict the Master Chief's image will be burned into a few of those by late-November, and a few developers will have improved physiques gained by carrying Xboxes to and from work on a regular basis. However the extrordinary amount of pizzas consumed at the average frag-fest will probably have an adverse effect on most physiques.
My division has a milestone a couple of weeks before November 9, so we shouldn't be too effected by Halo. Here's hoping we don't slip, else we'll be in trouble...