Matt could tell us what they are working on... but then he'd have to kill us. In response to some complaints at the halo.bungie.org forum about the recent lack of new screenshots, movies, or juicy update tidbits, Matt Soell has piped in on why mum is now the word:
Glad to hear that the insectile eradication program is proceeding apace, Mr. Soell. Now, about that wall-hugging hippo...The lack of major new stuff in the Halo Updates is largely because most of the stuff we're working on now is spoiler-heavy. As for the rest, there are only so many ways I can say bug fixes.