I don't support gun control to the degree to which it exists in Great Britain or in Canada but I believe some form of gun control should be practiced. It's only common sense. There was gun control in towns in the "wild west" for a very good reason.
Ownership of guns is not necessary to fight against a tyrannical government. In fact, it's somewhat naive to assume that if the US ever becomes a tyranny, that the brave patriots who choose to fight will do so with guns. It simply makes no military sense to do so. Such freedom fighters would probably employ tactics similar to those used by Timothy McVeigh or by the insurgents in Iraq. I'm not saying that guns wouldn't be useful, but their use would probably be less cost effective than the use of IED's or their ilk against soft targets.
A tyrannical government would probably have little use for limiting ROE's so any force armed with rifles and pistols and determined to fight "clean and fair" would probably get destroyed by artillary and air-strikes; any civilian non-combatant casualties will probably be touted, by the tyranny, as either being "acceptable" or they would accuse the patriots of using civilians as shields. Of course, engaging government forces in areas with high population densities is probably a smart thing to do, since any casualties caused by the government may result in a propaganda victory.
For some reason, many of the people who tout the ownership of guns as being necessary to fight a possible tyranny would probably be horrifed by the realization that, in such an event, they probably would have little use for their guns in such a conflict rather than to execute government soldiers who have been taken prisoner (keeping prisoners is rather problematic if you are a guerrilla force - see the Boer War for what eventually happens). Most of the damage would probably be accomplished through more cost-effective means by which the patriots could use their paucity in numbers to advantage.
This is, of course, a pretty complex subject. I just wanted to point out that assuming that private ownership of guns was somehow crucial to toppling a tyranny (an argument used by many gun advocates) is somewhat naive and ignores the realities assymetrical warfare. There is also a sort of "gun fetish" culture that also exists in the US whereby people who do not need guns seek to acquire them simply for the sake of owning them and resorts to circular logic in order to justify their right to own said guns. With that being said, I don't believe that guns should be banned but that there should be some sort of common-sensical ordinances to regulate their use; of course, this runs afoul of how the political process often works in democracies.