We can find a mix of leadership styles across the US government, but many of the star leaders we have today, especially in the military and in other operationally-minded places, have adopted a flat approach to organizing their staffs. If you read any of the profiles of Gen. McChrystal when he was appointed Commander, ISAF, there are several mentions of his preference for a small, flat staff. We have quite a few highly effective small groups closely associated with a particular senior leader, and they will often provide a lot of value to whatever they are working on.
You also hear McChrystal and Petraeus talk a lot about letting the troops in the field take the initiative and learn. In Linda Robinson's book Tell Me How This Ends, there are several examples where Petreaus meets with captains and lieutenants for a run or a briefing and he tells that they are empowered to do what they think is best, despite the military bureaucracy. He knows they understand how to fight the war in Iraq better than many people in Washington, because they've learned so many lessons by being there, and they use places like http://companycommand.army.mil/ to spread the knowledge.
Unfortunately, we haven't seen whole organizations and departments adopt flatter approaches to managing their people. It's very hard to break the boundaries between policy offices. Richard Holbrooke has put together an interesting group of people in the form of an interagency team, but it's hard to tell how they fit into the whole Afghanistan (and some will say Afpak) issue, given the plethora of players surrounding it. But if you can find information about how it is managed, you'll find that it's a small and flat team with people from across the US government.
In terms of using social technology, I think ODNI and CIA have probably gone the furthest, with A-space and Intellipedia, thanks to the leadership of Mike McConnell, Michael Hayden, and Dennis Blair. The initiative to use social technology in the intel world came from a guy named Michael Wertheimer: http://tinyurl.com/yd822pa. However, as we saw with the Christmas bombing attempt, there is still a lot of work to do.
Basically, people are stepping out of the box, but just barely. Where they do, it's very encouraging though. I think that's what you'll find in your examples.