McChrystal is out; Petraeus himself will take over in Afghanistan.
I'm sure there will be a lot of analysis. Off the top of my head, I think it may represent the best of a bad set of choices. To leave McChrystal in place on the grounds that his value outweighed his insubordination would undercut civilian control of the military; a rebuke without removal would weaken McChrystal without strengthening the President.
By naming the one man who is as thoroughly identified with counterinsurgency as McChrystal was, the commitment to the doctrine is clear. It's unfortunate that Petraeus recently had a fainting spell in front of Congress, but his stamina is legendary.
Petraeus also salutes and takes what is really a demotion, from CENTCOM to a theater within CENTCOM, but also assumes a combat command at a difficult time. If he doesn't burn out, he'll be either Chief of Staff of the Army or JCS Chairman someday.
McChrystal, who could well have eventually been Army Chief of Staff, won't be. The mystery remains: what was he thinking?