Numbered 1.0004 - just how many patches are they planning on producing? - the update adds a dedicated server mode, some bug fixes and a large number of optimisations to the graphics engine. These optimisations will add up to 10-15% on to the framerate, regardless of graphics card or driver version.
Benchmarketeers: this is a good thing. The release notes suggest that part of the increase in performance comes from moving some calculations of detailed objects to a second core in your multi-core system, should you possess one. Another optimisation re-writes some of the game's graphics shaders for better performance. A new network packets wrapper was also written which will result in a better ping in multiplayer and a less congested network.
You can grab the patch here. Get out those FPS counters, folks. ยต