Statistics

Statistics are a system that got added to Minecraft in the 1.5 update. Notch talked about statistics (along with Achievements) on his March 18th Blog Post.

You can view a video of the achievements and stats here

Statistics on the Minecraft.net profiles
Notch also commented that the plan is to show achievements and statistics on the profiles of the Minecraft.net site.

Statistics in the raw files
Taken from stats_US.lang in the lang folder in minecraft.jar

Times played

Worlds played

Saves loaded

Multiplayer joins

Games quit

Minutes Played

Distance Walked

Distance Fallen

Distance Swum

Distance Flown

Distance Climbed

Distance Dove

Jumps

Items Dropped

Damage Dealt

Damage Taken

Number of Deaths

Mob Kills

Player Kills

Fish Caught

Blocks Mined

Items Crafted

Items Used

Items Depleted