Watched the DC last night and I'm sad to say I have NO IDEA what it adds. I saw Zodiac once theatrically and once on DVD, but I couldn't definitely identify any new footage. Not saying it's not there - the movie clearly runs longer - but I sure couldn't figure out what changes occurred.
Hope others can elaborate on the alterations when they get their copies.
At least this DVD eliminates the annoying jaggies and shimmering of the prior DVD...