Till now -- till Hezbollah. Hezbollah chose when and where and how they were going to fight Israel. Here are the lessons they learned. Read'em and weep, because they work just as good against US armed forces and tactics as they do against the IDF:
First, most important lesson: take the defense tactically, the offense strategically. This ought to be a familiar doctrine to any American war buff because it was the policy behind most of our great victories, like Bunker Hill, New Orleans, and it's what kept Lee's Army of Northern Virginia on top against bigger and better-equipped Federal forces until Gettysburg -- and the only reason Lee lost there was because he abandoned the policy like a fool. Hezbollah took the offensive strategically by prepping the ground, Southern Lebanon, with a network of underground bunkers, then picking its moment to attack Israel while the IDF was busy kicking ass down in Gaza. The IDF, already under pressure for not rescuing that soldier kidnapped by Hamas in Gaza, charged over the border right into the trap.
Once they'd provoked the massive attack they hoped for, Hezbollah assumed the defensive, sticking to their bunkers and launching an incredible number of guided and unguided missiles against the Israelis. The most devastating weapon they have is the RPG 29, the newest Russian version of our old friend the RPG 7. The RPG 29 seems to be able to knock out the IDF's MBT, the Merkava 4. That's a big, big blow to the IDF, because the newer Merkavas are supposed to be invulnerable to anything but huge shaped charges laid as mines. They're equipped with all the latest tricks in anti-missile defenses, like reactive armor and screens that are supposed to make the warhead detonate prematurely -- kind of like premature ejaculation for RPGs. ("Oh jeez, sorry honey, I guess I just got too excited, your turret's so damn sexy....") The RPG 29 has a simple but effective counter for all this last-ditch defensive stuff: a tandem warhead, where the first warhead blasts the reactive armor or screen and the second, the really deadly shaped-charge one, has a free path right into the tank. By sticking to their bunkers, where they could fire from safety at the Merkavas, the Hezbollah antitank teams destroyed the Merkava 4's rep in a few weeks.
At sea Hezbollah used the same strategy: use guided missiles against high-value targets. Israel has been used to having control of the Mediterranean, and using its navy as low-cost, mobile artillery to blast enemy positions (and picnics). Hezbollah served notice that them days are over by hitting an Israeli gunboat with a guided weapon of some kind. It's not clear what they used, either an Iranian antiship missile or something homemade, some kind of model aircraft carrying a few pounds of C-4. Personally I'm hoping it turns out to be the Ace Hardware version, some dweeb's model Cessna, the kind you see sad Asian kids flying around your local high-school parking lot on weekends, modified by the Bill Murray character in Caddyshack -- you know where he makes models of the gopher's little friends, "the harmless bunny rabbit" and so on? I'm not sure what a Hezbollah model-airplane dweeb would make out of plastic explosive -- in fact, I'm not sure what a Hezbollah dweeb would look like if one even exists -- but it'd have to be something resembling IDF naval vessels' little friends, like a claymation US congressman with a sack of money in his teeth, maybe. Whatever it was, the contraption worked: killed four IDF crew, set the gunboat on fire, and taught the Israeli Navy a little respect.
Second Lesson: When you're fighting a force that depends on firepower and air power, DIG IN. Hezbollah has been tunneling out Southern Lebanon like those Caddyshack gophers from the first day the IDF vacated the area. They built reinforced bunkers, some with AC, designed to withstand air strikes and be used as firing positions for those new-generation anti-tank weapons. Just think for a second and you'll see that if you don't need to move, and stay underground like the Cong in Cu Chi, airpower can't touch you. The IDF kept waiting for Hezbollah to move aboveground but got nowhere, because the Hezzies had what the Germans call "fire discipline," the special kind of guts you need to stay still and not fire till the enemy's real close. The hotheads in Hamas have the more obvious kind of guts, attacking the IDF with small arms and old RPGs from the back of a pickup, but that kind of courage don't cut it no more.