Editing a wiki is the kind of experience that is much more valuable to employers than social networking or most common online activities for most occupations, with the exception of marketing/PR-specific roles. Collaborative work on a wiki involves teamwork, research, editing, effective communication, and a whole host of other skills that are useful in a business setting. Blabbing to your friends on Facebook or Twitter doesn't develop these skills.

It's certainly an advanced skill compared to taking a Facebook quiz, but I think it clarifies the assumptions people have about young people, that they know all the computer things because they grew up using them. That's really not the case.

If you want an alternative metric, something like 1 in 3 entering freshmen don't know what the BCC feature does in email. We know that pretty much everyone uses email daily (despite what they tell parents and teachers), so it cannot be that immersion alone leads to proficiency, or that proficiency cannot be learned as an adult.

If you want to rate candidates by skill, by all means do so, just don't go the extra discriminatory step of saying old people by definition cannot pass your measurement, and that young people by definition do.