Plausible-sounding criticism of Randi’s One Million Dollar Paranormal Challenge?

I’m currently working on a chapter for the book on how supernatural claims can be scientifically investigated. I’m including a few paragraphs on James Randi and his One Million Dollar Paranormal Challenge (link is to Wikipedia). For obvious reasons, it would be nice to include a brief response to some criticisms of the challenge, but I’m not sure where to start. I’m worried a Google search will just return nuttiness.

The Wikipedia article’s discussion isn’t bad, and I may just track down the primary sources, write a quick summary, and call it a day. Or are there other points that would be more worth my time? Does anyone reading this have their own reservations about the challenge?