Actually there is quite a bit of truth in what deacon says. One gallon of gasoline, given the proper conditions has the same explosive potential as one stick of dynamite, but... a full tank really has no chance of exploding. Although a nearly empty tank could go off like a small grenade.

Gas tanks can explode, I have seen a tank on a small dirt bike explode, fortunately no one was on or near the bike at the time it went off, but it certainly left an impression on me.

Hollywood does over do things, and the chances of an explosion are rare, like getting struck by lightning, but the chances of getting severely injured does exist if the fuel system on anything that we have to be so closely situated to has some sort of a problem. (Pour a little gas down your pants leg and light it. You might find it difficult to have it extinguished before you'd like. (Actually, please don't pour the gas down your leg.))

Saddletramp1200 is bringing up a good point here, and I've known many to just patch or ignore a fuel system problem, that's not the best course, maintain and repair your fuel system correctly, not only for safety purposes, but it will eliminate other problems as well.