How do you defeat a force armed with the most technologically advanced weapons? Easy: you wait for them to get out or off of the equipment. In Yugoslavia, (future) Marshall Tito was asked about how his partisans armed with old rifles would defeat the Germans, who were armed with new tanks. He replied: when a German gets out of his new tank to take a pi$$, my partisans will shoot him with an old rifle.
Guerilla operations are cheap, at least monetarily. An occupying force needs upwards of 10 men for each guerilla, and even then many guerilla attacks are successful. As has been pointed out, the WILL to fight is far more important than the tools one brings to the fight. Just ask the American military governor of Vietnam or the Soviet military governor of Afghanistan, they'll tell you.
As Balog has mentioned, officials of a tyrannical regime in a nation with a high rate of civilians being armed have a lot to fear. Let's look at how many people there would be:
1) There are roughly 80 million gun owners;
2) During the Revolutionary War, roughly 3% of the populace actually took up arms against the Brits;
3) Assuming that we are only 10% as brave, per capita, as our Revolutionary era forefathers, 0.3% of gun owners would actively take part in a revolt (that's only 1 in 333 gun owners).
4) 80 million x 0.003 = 240,000!!
Heck, if only 1/10 of THAT number, less than 1 in 3,000 gun owners, decided that it was open season on tyrants and their servants, you'd have 24,000 rebels. These 24,000 would be the most highly motivated, they'd probably be amongst the most skilled with firearms (many courtesy of Uncle Sucker), they'd probably have extremely high quality weapons (i.e. bolt-action rifles that can reliably hit human torso-sized targets past 500 yards) and, best of all, they'd blend in to the overall population because - guess what - they would be a microcosm of their individual communities.
Does anyone remember what 2 idiots, one of whom was untrained in the use of firearms, did to the DC area with a semi-auto that was never used past about 100 yards? Remember, several thousand police and federal agents - aided by satellite technology, if the reports are true - were looking for them, and they brazenly or carelessly left evidence to be found. Now scale it up: 24,000 (or, lets be real dramatic, 1% of that number or only 240 - which is only 1 in 333,000 gun owners!) people trained as marksmen by the military, armed with accurate, sighted-in bolt action rifles, decide to make trouble if the fed.gov instituted a gun confiscation scheme. And they aren't insane killers with no agenda but murder for murder's sake, but patriots motivated by a love of their nation and their liberties. I'd say that the country would be tied up but good, and that the economic consequences of such an action would dwarf the physical impact of even this very low number of shooters. Imagine, for instance, that a few of them decided to take out trucks bringing food or fuel from the heartland into the coastal cities. Truckers would go on strike, and the big cities would feel the pain of food and fuel riots very soon. To take Balog's scenario a bit further, suppose that some of the 240 gun owners had lost family in raids. It is not too hard to imagine that they'd be motivated by revenge, and decide to take out family members of various government officials. Imagine if some of them were ex-Special Forces types - would YOU want to be a gun-grabbing politician or media type (yeah, they'd be targets, too).
The long and the short of it is that even a small group of highly motivated and skilled people can do enormous damage to a behemouth like the fed.gov, one pinprick at a time. As pointed out in UC, the active IRA is only 100 people located on an island about the size of Arkansas, and it has given the Brits fits for over 30 years, despite the latter's complete dominance in the quantity and quality of men, weaponry and sensing technology. A few hundred or a few thousand rebels might not seem like much against the resources of the fed.gov and the states, but when operating throughout a continent-sized theater where over 250 million guns exist (not to mention lots of high explosives and related equipment), the odds are not so great.
