After a bit of pestering, Bungie's Nathan Bitner offered two interesting little Halo tidbits (quite possibly so I'd stop bugging him ;). The first comes after some discussion about terrain bump mapping:

Just for the record, Jason has stated that the water is both texture-mapped and bump-mapped. It's a pretty cool sight to be quite honest ... our office manager thought he was showing off vacation pictures ...

Bump mapped ripples and waves maybe? Can't wait to see it in motion... the other question was about night action in Halo, to which the reply was:

Well, it certainly would be strange to have headlights and flashlights if you never had a time or place to use them, right? ;-)

Point well taken. Many thanks to Nathan for fielding these questions, which will be added to the FAQ shortly.