Dr. Tony Tether, the longest-tenured Director in DARPA’s 50+ year history and a target of frequent criticism from the computing community and the university community for the direction the agency has taken under his leadership, is apparently out as of February 20, 2009. Tether made the announcement in an email to DARPA staffers:

The Time to Go has Been Settled
As you know, I had said that I was asked to stay on at DARPA until replaced.
It turns out that that was not the case. 
I was informed last week that the Administration had decided that I was to leave now with February 20th as a two week notice.
So it’s over.
But it has been a good ride and we have many, perhaps thousands, of technology developments most of which are yet to come, but also many which are out being used saving our Soldiers lives yet making them far more effective than the adversaries they face.
I want you to know that I am proud of all of you, current and past, and will never forget what you have done.
Once I know what I am doing, I will let you know.
God bless all of you, and most of all, God Bless America.
Tony

It’s not yet known who will replace Tether. A number of folks from the computing community have done some thinking about what a “re-envisioned” DARPA might look like. CMU CS Department Chair and CRA’s Government Affairs Committee Chair Peter Lee and Berkeley’s Randy Katz put together those thoughts in a piece for the CCC in December called Re-envisioning DARPA (pdf) that certainly seems worth reading again.
As we learn more about this change in leadership at this critical agency, we’ll post it here!