Minecraft v1.6 was released today.
+ Added Nether support to multiplayer
+ The client will ask minecraft.net if the current login is valid. If the server says “no”, a warning message appears in the client. You can still play the game even if this happens.
+ Added craftable maps
+ Added hatches
+ Added tall grass in some biomes
+ Mushrooms now spreads (very) slowly
+ Added server property view-distance. Sets the radius of terrain updates (in chunks) to send to the players. Range 3-15, default 10.
+ Added dead shrubs in deserts
for a full list of the changes visit this site.