Yes, I have used Knoppix. I only had a play around with it, but there was a lot of useful tools on there, and I liked the idea of running an O/S from a bootable CD.
I just wish I had more time to get familiar with the tools!
I am busy with the CEH (Certified Ethical Hacking) course and was wondering if anyone out there has done it and uses Knoppix STD for security checks/testing?