Notch recently revealed more information regarding the 1.8 Adventure Update. The following things have been confirmed for the update's release:
•NPC Villages
•Randomly generated dungeons
•New biome code
•Fully functioning Creative mode (with Creative-type access to server mods/admins)
•Critical hits
•Sprinting
•More farming options
•Brightness slider
He also mentioned that mod support was definitely being worked on, but that information on the update as a whole would be kept under a tight lid, to avoid revealing too many surprises.
We will continue to update the community as information becomes available.