We had the same discussion over at JavaJunkies a while back. To echo my thoughts there...

I believe that the experience system is based on involvement in the community, not just on perl related knowledge. I'd far rather see people gain experience for contributing to the site and helping others out than just passing a test.

Note that my stance on this issue has absolutely nothing to do with the fact that I'd most likely lose XP if we switched over to a test-based system ;-)