"against an Iraq with no air defenses"
They had 'no defenses' because we took them out! :-)
If anything our airpower is much better than in 1990, with JDAMs and other options we lacked then. Iran 2006 may be better than Iraq 1990, but are far from a match to US.
"defenses, useable SCUDs etc after years of sanctions"
Ah, that's your mistake ... I am talking about 1990, not 2003. Our current situation is somewhat similar to 1990 IMHO. Iraq was stronger in 1990 (or perceived as such), and you may recall, had SCUDs that were able to reach Tel Aviv.
They did little real damage.
"robust Iran, with an apocolypse-desiring madman for a leader." .... Iran may be 'robust', but they are not invulnerable to a US air strike. The option I am sure is on the table. And why not? Reagan against Libya 1986. Clinton several times, including the air war against Serbia.
It's cleaner than a ground war (viz Iraq).
My point is simple: The air strike option WILL work. It will delay Iran's pursuit of nuclear weapons and it will not have great collateral damage.
Let's hope you're right. I still don't think a president will risk it, not after the merciless pounding Bush has taken.