The build number is in the top left version on the main menu, to the left of BLDW. It should say 0526 or similar.Where can I see what version of the game I have? I kinda miss manual patch downloading. It made me curious to go to the forums and see what new stuff was introduced with them...
You can see the build notes for new builds as they come out here: http://forum.wmdportal.com/showthread.php?646-Build-Release-Notes-(NOT-FOR-BUILD-BUG-REPORTS!)