When I was just starting to do concert photos years ago, I accidentally shot Derek in Motion
. I loved the effect and have been trying to reproduce it since. It works best with guitarists, because there's a lot of little metal bits on the neck that reflect ambiant light, and because the motion is often directional. This is a 0,5 second exposure.
The anonymous guitarist here is Monophonics' Ian McDonald. I'll be posting more recognizeable pics of him soon, but I thought I'd share this devilish shot!