The Dog that Didn't Bark
Despite every Western media outlet which has mentioned PM Nour al-Maliki's two day trip to Tehran including a claim that he would confront Iran over alleged meddling in Iraq, public statements from Maliki's office at the close of the visit are utterly devoid of any mention of the issue. Instead, Maliki has gone out of his way to assure the Iranians that his country won't be used for an attack on theirs and the Iranians for their part have said that they consider a peaceful Iraq to be essential to their own security.
That's really not all that surprising, although you wouldn't think so from reading Bush administration pronouncements or mainstream media stenographic repetition of the administration's talking points. When push comes to shove, the real story is that the Iraqi faction most backed by Iran is the Iraqi government - and that Sadr is a looser cannon who is far less under Iran's control.
And despite the US "suspecting" that every captured Shiite arms dealer or insurgent is part of those "Iranian-backed special groups", often purely on the circular argument that they're Shiite, there's evidence to suggest that a more of the weaponry washing around Iraq was "mislaid" from US-provided stockpiles than came from Iran. In neither case. of course, does the presence of black market entrepreneurs selling that country's weaponry to insurgents prove that the country's government is deliberately arming insurgents.