1. Most of the time it works.
2. If you get it wrong, you really
screw up.
3.
Screw ups are bad. Screw ups like
blowing your
$200 Motherboard.
First thing, don't ever try to push your
processor to
insane speeds without
proper cooling. A
P2 400 should not go to 800. A 200% increase is
virtual suicide - your processor would, on average, be running at 150
Degrees Celscius.
Your computer won't get past the loading of you
OS. After you've blown your motherboard, start
weeping like a girl.
Overclocking can be
lethal,
Not like a gun is lethal, but like a brick wall along a highway is lethal.
  - Douglas Adams, The hitch hiker's gude to the galaxy.