Eric Trautmann notes in his blog that he got his last payment for his work on The Art of Halo just recently-- and ahead of schedule, at that. Also, it seems, this means the book may be out soon:

I'm also given to understand that the book is due to arrive in Del Rey's warehouse system very soon now, which means I may actually see it soon. (A variety of Bungie folk decended on it during it's layout phase and I opted to stay out of the way; this is cool from a stress-reduction standpoint, but not so cool from a "Hm...I wonder what the hell the book looks like" standpoint.)

[Checks watch, waits to see how long this tidbit takes to get onto a Halo fansite...]

Eric: about three hours. Sorry for being so slow, we'll do better next time.

UPDATE: Eric added another update; he's actually received his copy of the book now.