I used to complain about people using They as a substitute for he/she (or the more compact s/he). Which is strange for me, because I tend to be a descriptivist when it comes to language rather than a prescriptivist. But at some point, I caught a NY Times article using They for the singular. which bugged me. This new column argues that using They as singular was common until a feminist grammarian in the 1800's convinced everyone to use He for the genderless singular pronoun.
Up to grad school, I still stuck to the old rules and used he exclusively, but that raised the umbrage of a feminist education prof of mine, so I have adopted the economics standard of alternating, though that normally means defaulting to she especially for people in positions of power. Now, it is nice to know that maybe using They is ok.
And come to think of it, at some point, it became ok to use the 2nd person plural as a singular (You used to be plural, Thee and Thou was the singular form). So why not use They for the singular as well.
(I used to stick to using he/him exclusively as I had been taught in grade school until getting chastised by a feminist professor in grad school, so now I adopt the alternation which seems to be the norm in economics [the norm also requires the gendered pronoun used to defy stereotypes. For example, the manager is always a she])