This move is obviously a big win for open source. As John Scott of Open Source for America (a group advocating open source adoption by government, to which I am an advisor) noted in an email to me: "This is great news not only for the use of open source software, but the validation of the open source development model. The White House's adoption of community-based software provides a great example for the rest of the government to follow."
John is right. While open source is already widespread throughout the government, its adoption by the White House will almost certainly give permission for much wider uptake. Particularly telling are the reasons that the White House made the switch
Thoughts on the Whitehouse.gov switch to Drupal [radar.oreilly.com]