Coffeemug beat me to my comment about this post. We're an all Ruby shop, and I don't think we've ever hired someone who (a) knew Ruby well coming in and (b) wasn't up to speed in under a week. If you're strong with Python, Perl, or Lisp, you will do fine in Ruby.
It is not a buyer's market for Ruby devs. Any post that suggests you screen a candidate based on whether they know what the "||=" operator does is offering bad advice.
The precise semantics of ||= were subject to a longer discussion on ruby-talk. I don't think it's really that important whether it expands to 1.) a || a = b or 2.) a = a || b, is it? So all you would know about a person giving answer 1) is that he/she was subscribed to ruby-talk at that time.
I find his answer to his own questions about proc/lambda/blocks unsatisfying since that would be IMHO a good question to identify people who know ruby well.
It is not a buyer's market for Ruby devs. Any post that suggests you screen a candidate based on whether they know what the "||=" operator does is offering bad advice.