Some say its the wood. Mahogany will give you a warmer, deeper sound; ash is a little brighter, etc..
Then you have your pickup fanboys, who say a great pickup will make any cheap parts-o-caster sound great. Then there's amp techies who drool over schematics like it was a centerfold, and the down-home old schoolers who insist that good tone comes directly from player's fingers and their ability to caress those wound nickel strands.
Debate aside (I'm a "in the fingers" kinda guy), Larry Lashbrook, of Lashbrook Guitars, has pushed the argument for pickups to a new level. Recently, Lashbrook has developed a new piezo system that he believes is so good, it can make any guitar sound good, no matter how bad it is.
To put it to the test, Larry actually took a concrete block, bolted a neck to it and stuck his piezo in it. Now, I know what you're thinking, "WTF?!" Yea, that was my reaction too... but after hearing it, I'm really impressed. (But not nearly enough to want to buy a concrete guitar)
It does sound a bit processed, but come on, its a freaking block of concrete: one of the least resonant materials out there. Props to Larry and the guys for breaking the mold and demo-ing their product in a really cool way.
Check it out, tell me what you think: