Iran has made nothing but verbal threats. At this stage of the game, they have little to show and a lot to bluff with. You cannot use the doctrine of preemptive attack to solve every problem - that would lead to everyone eventually ganging up against the USA and launching a full out attack.
http://www.cnsnews.com/ViewForeignBureaus.asp?Page=/ForeignBureaus/archive/200611/INT20061117b.html You can see everyone wants to shut down the dialogue; they want war. As it stands, the Iraq war is about to tip over $502 billion, we are under record deficits, and foreigners aren't buying t-bills like they used to.
We've already helped to undermine Lebanon, Iraq is in shambles, our military is seriously over-extended and burned out, recruiters can't get new heads in and there's been talk for awhile about reinstating the draft.
Let's think about this for a minute as we're heading for a cash crunch. The dollar's been falling in value for a few years, which doesn't make for the USA to be a great t-bill opportunity to foreign investors. Should the dollar continue to slip, t-bills will be cashed out. What would happen if all those bills were called in tomorrow? Americans would have to come up with thousands of dollars they don't have to pay the piper.
I say let's not add to the financial and political instability. It's time to stop letting wild rhetoric determine this country's course.
As for the argument, "should we stand by and let them do something before we act?" The country always survived prior wars when we were first attacked. Preemptive is only a recent policy.