Iran and Israel
Anyway, suffice to say that it can pretty much take out anything you could think to build to protect something valuable, like nuclear weapons and facilities. This message was obviously meant to send a message to the Ayatollahs that if Iran does fully develop its nuclear weapons, they won't be around for long. But is this an empty threat? The IAF has the capability to strike with the GBU-28s with its F-15Is (its version of the USAF F-15E). However, capability to carry a munition does not mean you can strike anywhere, since the IAF does not have any air to air refueling capability. Making the assumption that Israeli F-15Is will have a combat radius of a little over 1000 nm, carrying just CFTs (Conformal Fuel Tanks, sleek fuel tanks mounted along the side of the F-15), one GBU-28 on the centerline, and two external fuel tanks, and flying at low level through Jordanian airspace, I used this map to calculate that it is approximately 900 nm from Israel to the Iranian nuclear facilities at Bushehr. However, this assumes that Israel is willing to bust Saudi airspace; if so, the F-15Is would have to fly at low-level, severely curtailing their range, making the approximately 1800 nm round-trip a dicey proposition. Breaking Saudi airspace should be avoided if at all possible. Alternatively, the IAF could opt to fly through Iraqi airspace, since it is unlikely the Iraqis would notice, while any American radar units would turn a blind eye. However, this makes it a one-way distance of 1200 nm or so, meaning this is even more dicier than the Saudi option, range-wise. The F-15Is would be able to egress Iranian airspace, but would probably be unable to return all the way to Israel. So, where do they land? Saudi Arabia is obviously out. Bahrain does not have a U.S. Airbase, while Kuwait is unlikely to grant the Israeli aircraft permission to land at a U.S. Airbase. Despite being extremely friendly to the United States, both Iraq and Qatar are also unlikely to grant the F-15Is permission to use their soil. The wild card in this whole scenario is if the U.S. decides to allow the F-15Is to refuel from a U.S. tanker. However, IAF aircrews, as far as I know, are not current in their air to air refueling training. So, for this to work, IAF aircrews would have to be trained on refueling procedures. In addition, this option removes the deniability that a straight IAF operation would have afforded the U.S., meaning that the U.S. might as well do the strike itself.
Then there's the issue of escort. While air to air escort should not be an issue, in order for greater precision, SEAD (Suppression of Enemy Air Defenses) escorts, also known as Wild Weasels, will be necessary. This increases the number of aircraft needed for the mission. The Weasels are necessary so the target can remain lazed while the bombs are on the way; aircraft are vulnerable during the time it takes from bomb release to impact. The only other alternative is for commandos to be inserted to laze the target; this is really only a realistic option for targets relatively close to the sea.
So, at the end of the day, there really are no good options. Either the U.S. provides air to air refueling of the F-15Is, or the IAF will have to risk losing some or all of the aircraft after they run out of fuel. Israel only has 25 F-15Is to begin with, so I can't imagine large losses would be acceptible for the carrying out of the mission. I won't go so far as to say that the GBU-28s represent an empty threat, but the Israelis will have to accept some pretty steep losses for the carrying out of the mission.
UPDATE: (newly minted) 2Lt. Jarred Fishman (aka The Air Force Pundit) sends an email detailing that, in short, the IAF does in fact have a 707 converted to be a tanker. I did not know this. In my defense, I checked scramble.nl, which tends to have a very accurate order of battle for air forces. However, in my haste, I completely missed the '707 variants' listed as being based at Tel Aviv. This certainly changes things. All the IAF needs is a base for their 707 to stage from, somewhere on the Gulf. I definitely think that Qatari or Kuwaiti officials would be much more likely to allow a "harmless" tanker to stage from their soil, rather than a fighter-bomber. So, basically, disregard all of the above.