Seems like an opportune time to resurrect this thread. Oh, and to add that I put spaces around all my em dashes, and I don’t care what style guides say or don’t say — it’s just much more pleasing to the eye with the spaces. I don’t use grammar in order to comport with style guides. (Who died and put ‘style guide’ writers in charge?) I use grammar exclusively to try to avoid jarring awkwardness for a reader; therefore, I would never consider it correct to follow a grammatical rule that results in an uglier or more awkward construction. To me, that sort of ‘correctness’ entirely defeats the purpose of grammar, but YMMV on either the ugliness or the purpose.