Im still convinced the lower case use of google, facebook etc. (which occured more than once in the comment) is important - especially as there is one Google at the start of a sentence - indicating it is intentional/common.

That's why I personally discounted many from your first list (plus the fact I know a few are native English speakers)

Run it through a Markovian classifier like CRM114 (or, if that's too expensive, just do it for the likely candidates identified by your naive Bayesian classifier).

Hey hey, two guesses each :)

Now I have to add my third from the list: nostrademons.

This challenge is a bit flawed in that we have no way of knowing if the anonymous poster is willing to ever confirm that he/she made the post, isn't it? Not to state the obvious but it just seems that even if a great amount of technical work is put into this, you'll never know the answer unless the person in question agrees to participate.