BBC reports (check out the video at that page for "before" and "after" pictures):

The photos of [Lee Spievak's] severed finger tip are pretty graphic. You can understand why doctors said he'd lost it for good.

Today though, you wouldn't know it. Mr Spievak, who is 69 years old, shows off his finger, and it's all there, tissue, nerves, nail, skin, even his finger print....

Mr Spievak re-grew his finger tip. He used a powder — or pixie dust as he sometimes refers to it while telling his story.

Mr Speivak's brother Alan — who was working in the field of regenerative medicine — sent him the powder.

For ten days Mr Spievak put a little on his finger.

"The second time I put it on I already could see growth. Each day it was up further. Finally it closed up and was a finger.

"It took about four weeks before it was sealed."

Now he says he has "complete feeling, complete movement."

The "pixie dust" comes from the University of Pittsburgh, though in the lab Dr Stephen Badylak prefers to call it extra cellular matrix....

Now if only he could regrow the "." after the "Mr". Thanks to InstaPundit for the pointer.

UPDATE: "Junk science," reports an English professor of hand surgery. "It looked to have been an ordinary fingertip injury with quite unremarkable healing. All wounds go through a repair process." Well, rats. I still hope the story pans out, though this criticism suggests it might not.

FURTHER UPDATE: Commenter PatHMV (Stubborn Facts) reports that Scientific American also mentioned the story, and reported that "the injury was treated with a protein powder that might have aided regeneration by acting as a scaffold for regrowing tissues" -- not a ringing endorsement, but also a suggestion that this isn't just junk science.