Version 2011-02-12 (compatible with previous) has:

• Per-server textures. Replace terrain.png and players connecting to the server will see it.
• Sun and moon.
• More options: key bindings, view distance, sound off. Options are saved.
• Server setting to disallow freemove.
• Small speed improvement.
• Chat scrolling.

A new release has been issued (2011-02-02), it now has Night time. Shadows must be enabled via the in-game options for this feature to work

Antivandal:

World is split into two sides. On one everyone can build, and on another password is required. To host an antivandal server, set BuildPassword in ServerConfig.xml and use /login [password] command to play.

release date 24.01.2011

This latest version now brings back minecarts, it also reduces game lag around the save game points

New version (2011-01-15) is around 3x faster at high view distance. At view distance under 256 (F key), game is up to 10x times faster than previously.

There is less fog.
Fog 32 (old version on the left)

Fog 64

Details about optimizations: forum.