This was coppied from the TF2 Blog:

The Eyelander holds to a principle all one-eyed Scotsmen with no depth perception have known for years: you don’t kill a man by mucking about with rifles, arrows, rocks, or other long-distance rubbish. You kill him by grabbing the biggest bloody sword you can find, running up nice and close to him, and chopping the dumb bastard’s head off.

Made with pattern-welded Damascus steel, this melee-slot weapon offers a guaranteed decapitation with every killing blow. Unfortunately, because it's haunted, it will suck away some of your soul: expect a decrease in your max health at the outset. However, once the blade feeds on neck, you’ll receive a boost in max health and speed. With each new protesting head you cleave (up to four), you’ll get healthier and faster.

The Eyelander will not deal critical hits unless used in conjunction with the Chargin’ Targe’s charge ability.

The Chargin’ Targe solves a centuries-old Scottish riddle, which is that shields exist. True, the shield might block the occasional sword blow. However, they are essentially weapons to be used for hiding behind, and this is a concept the average Scotsman does not understand. “If I were to pick up this cowering-plate, I would have to put down my second sword,” a Scotsman thinks. “And surely that is madness.” The Chargin’ Targe solves this riddle by turning the useless shield into a deadly weapon you can run at people with and then bludgeon to death.

The targe replaces your tried-and-true sticky bomb launcher, but offers some unique capabilities in return, especially when used with the Eyelander. Just equipping the Chargin’ Targe provides automatic +50% fire damage resistance and +65% blast damage resistance. But the Chargin’ Targe’s main perk lies in its name. Alt-firing will hurtle you toward an enemy at a punishingly damaging high speed (far faster than a Scout can manage).

Charging also boosts the lethality of your melee weapon. Land a melee hit during a medium length charge and you'll be guaranteed a mini-crit. Land a hit during a long distance charge, and your victim will receive devastating full crit damage.

Source: http://www.teamfortress.com/demomanupdate/index.htm#item_1