This was discussed some time ago in Web-based certification services.
I still think the main line of critique against web-based certification services like Brainbench is in essence a critique of formalized testing procedures (like multiple-choice tests) as such. This may have some merit, but in the end anybody arguing against formalized testing procedures will have to provide some alternatives when facing the decision on how to evaluate candidates for a given job. Usually these alternatives will be more subjective (face-to-face or even telephone interview, recommendations, etc.) and/or more expensive (assessment center, trial periods, etc.). For a discussion of some alternatives, see Interview questions.
Brainbench MVP for Perl