Certain Affinity is currently a staff of nine experienced developers, averaging 12 years of industry experience apiece, and are currently seeking an Art Director for team player number 10. Their first project will be finishing up Halo 2 multiplayer maps. Certain Affinity is "simultaneously building a game of our own" that we guess will be made using the Halo engine, once the team is acclimated to it.
What's amazing is that, from what we can tell, Hoberman's experience in the games industry revolves entirely around Halo. Despite this, Hoberman is able to assemble an experienced team with accredited backgrounds and track records for his studio. Never underestimate the power of a key franchise. Previous high-profile Bungie employee to set out on their own include co-founder Alex Seropian, whose studio Wideload Games adapted the Halo engine to make Stubbs the Zombie in "Rebel Without a Pulse," and lead producer Hamilton Chu, whose studio Giant Bite has yet to announce a project.
[Update 1: As many commentors have pointed out, Bungie moved from Chicago to Redmond. Sorry about the confusion!]