And he does a great job of it too, playing his acoustic guitar sort of like a hammered dulcimer. From two Canadian music TV shows, here's Erik performing Percusienfa: [download mpeg video (11 megs) or youtube it], and here's his performance of Airtap: [download mpeg video (12 megs) or youtube it]. Here is Erik's website. Thanks to Stark Effect!
For more unique guitar playing, here's a post from last May about Hans Coetzee, who plays guitar while using a teaspoon in his mouth as a slide.