And here is some new news: your choice of faction will also determine your prerelease card! If you side with Mirrodin, you'll get Hero of Bladehold, and if you align yourself with Phyrexia, you'll take home Glissa, the Traitor. This is subject to availability, of course.
While we're on the subject, we might as well show off the card that will be given out at the Mirrodin Besieged Launch Parties on February 4. Behold Thopter Assembly!