Notch has updated his blog to announce that the Minecraft 1.5 patch is now live! The update adds a full achievements system to Minecraft, and brings rain snow and thunder to its cuboid worlds. As a bonus effect,pigs struck by lighting from the thunderstorms will be transformed into zombie pigmen. You can see footage of the new weather effects in the recent Minecraft 1.5 trailer .
If you find any bugs in the update, fixes might be slow to arrive. Notch also tweeted about patch 1.5 to say "I'm not reading twitter or email until I've beaten Portal 2, I won't know about any bugs in it. ;D."