Minecraft wiki entry for Development_versions, associated text: Smoothed out the cliffs in shattered terrain a bit.
Coastlines and river banks are less likely to be intersected by aquifers.
Local water levels are mostly used in terrain that doesn't border a river or ocean.
Cave openings and ravines that intersect an ocean or river will mostly use sea level.
Inland low-elevation areas are less likely to have flooded caves everywhere.
Grass no longer generates underwater.
Reduced the chance of incorrect surface placement.
Reduced the chance of river biome generating in dry mountain gorges.