Megan McArdle feels strongly about it:
Let me make my position clear: In situations with a generic singular antecedent, "they" is not OK. It is preferable. The attempted abolition of singular "they" was a hypercolossal blunder by 18th- and 19th-century fusspots who thought grammar should follow the same sort of simple rules as a steam engine, that Latin and Greek grammars were a good model for English diction, and that in public-facing activity, men absorbed the women in their circle like a sort of social sponge. We should stop perpetuating their error. We should rip this rule from our grammar texts and obliterate it from our stylebooks. We should fling it down and dance upon it.
Consider the reasons that we are supposed to oppose singular “they” . . .