Benchmarking Expertise

Wikipedia defines as Expert as...

An expert is someone widely recognized as a reliable source of knowledge, technique, or skill whose judgment is accorded authority and status by the public or their peers.

Some pretty big phrases there! Let's just list them down for now.

• widely recognized
• reliable source
• judgement is accorded authority
• peers

Alright, on to the issue. I guess the debate of whether an expert is deemed an EXPERT by Qualification or Acceptance has been sufficiently settled. Refer the following for details:

• How To Become A Hacker- Eric Steven Raymond
• What makes good engineer?

What really remains to be settled is how we can benchmark a person's 'expertness'. I figure the four traits listed above could be a start, but most of them tend to raise questions. How 'widely' is enough 'widely recognized'? Just who are your 'peers'; people you work with, people of like mind?
I guess this is more of a controversy than a debate, but what the heck! :)