The game assumes that weapons are rigid, and that the whole whip moves at ludicrous speed rather than just the tip. What happens is getting hit by roughly 1 kg of supersonic metal hitting point on, and our dwarves get off lightly because 40mm autocannon projectiles are beyond the scope of the impact mechanics.
Whips are the ultimate can openers, deadlier than most blunt weapons and practically ignoring armour. Not desirable for ourselves as we never fight anything that warrants dedicated can openers: against goblin lashers, naked dwarves wielding steel blades should still be favoured. You can't rely on it though, as a single lucky hit can end the fight.
If you reduce whip size to 1-5 (metal tip, rest of the weapon just exists to accelerate it) you get more reasonable results - still good at disabling via pain, but it won't ignore armour.
Scourges are useless to wield and annoying to fight against. Velocity and small contact area enable them to penetrate most armour with ease. They're capable of cutting off small bits but not very lethal because of small size and low penetration depth - expect them to maim more dwarves than they kill. They aren't lightsabers by a long shot, but they'd satisfy George Lucas' amputation fetish just as well.
A more powerful alternative that's actually somewhat practical: morningstars. Heavier, better penetration depth, otherwise identical stats.
@ ponom: In the dwarf wiki, 'metal' and 'weapon' are useful entries. In actual gameplay, it gets very very complicated.