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
- 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.