Further to Benjamin's story about John Renbourn.
I know a few guys who take a bit of baking soda (sodium bicarbonate), and mix super glue into it and build it up in layers onto their existing nails. It looks a bit wierd, though, even after the obligatory filing down to size. But looks don't make the music, do they?

I normally use my existing nails, which are kept reasonably long on my right hand, and shaped (to my own taste), which doesn't make them any more beautiful, but makes them a hell of a lot more practical. If I need that extra brightness about the picking, I'll use the old trusty Dunlop steel picks.

B.