Its a decent tool if you want to look at a build order in the list view, but, as others have pointed out, the timings are way off. I still use it from time to time to try different playing styles but I never "play the build."
Also, the only good builds are the ones uploaded by the community. This is a good feature. Id like to see a simple filter system though for race and build type (i.e. aggressive, defensive, mass air, etcetera).
The timer would be cool if it operated off of the time of your game; if it was linked the the computer somehow.
Montasaurus about Build Commander for StarCraft 2