In reply to:

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To be honest, there's some times when it's useful to know how ethernet works. They're few and far between, but it you don't know when it happens, you're lost

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Agreed.
I think the "who cares how it works" thing depends on whether you want a job fixing stuff
If you don't know how it works, how on earth do you expect to fix it.

But to answer the orignal question.
With any certification, it depends on what you want. Do you just want the certification or do you actually want to learn something?
It is possible to take a ten day course and become a CNE or a MCSE in a month. But you learn squat that way.
If you just want the cert, go out and buy the Exam Cram type books and cram, cram, cram!
If you want to learn, go on the course, get the hands on and the interraction with other students. Then take the exam.