I think it has calmed down because al Sadr fled to Iran and told his militia to lay low for now.
That may be as a result of the surge but I seriously doubt that. I think the ROE have changed and some bellybutton was about to be or is being kicked. The public announcements of Iranian arms being found around Iraq probably had its desired effect and al Sadr was probably called home by his Iranian masters to chill things down.
That said, I think Sadr will be back along with his militia. They only have to wait on the Dems to set a timetable, don't they?