The Iranian parliament speaker, Ali Larijani, has called the Iraqis to reject the US security pact.
He said Washington's goal was to "strengthening comprehensive U.S. hegemony in Iraq." and he called for continued resistance: "The Iraqi nation and parliament should realize that the time for resistance is not over yet,".
That should give pause to those who bemoan the massive influence of Iran in Iraq. But why would Iran be opposed to a deal that effectively makes Iraq a nation independent from "US meddling" in about 2-3 years if they thought they could control it? The logical conclusion is that their influence is not that deep inside Iraq despite religious similitude with the new rulers of the country; else they should welcome the withdrawal of the US.
The reality is that Arab Iraqis, even Shiites, see Iranians as Farsi foreigners. During the Iran-Iraq war, Shiites and Sunnis fought Iranians side by side and there are no history of widespread Shiites opposition to the war based on sectarian arguments. Iraqis and Persians might share a religion but there does not appear to be any sign that the former will be submissive to Iran. We saw the relevance of Iran's opposition in the cabinet vote which went 27-1. The lone dissenter was Sunni, so the odds that he voted no because of Iran pressure are, let's say, fairly low. We will see what kind of influence Iran has in the parliament vote, but I doubt it will be impressive.
Now that is not to say that Iran will not have an influence in Iraq. It is one of the major power in the region, along with Turkey and Saudi Arabia, and it will have more power than during the Ba'ath years. But those hyperventilating about how the US gave Iraq to Iran can calm down; Iraqis are proud enough not to let foreigners run the show.
There are a few caveats to my argument. Ali Larijani is not Ali Khamenei or Ahmadinejad, what he said should be taken with a grain of salt before we assume that it is the position of the Iranian government. Also, it is possible that Iran oppose the deals because they believe if Iraq waits until BO takes over, it will get a better deal and a faster withdrawal. But it is hard to see why they would get worked up on a 6-12 months earlier withdrawal; the end result would be the same.