singular they have popped up again. Andrew Sullivan is currently acting as a conduit and because his blog is so popular, he has the ability to reinforce this issue with a wide audience. To his credit, Andrew says "I often use her as a generalizing pronoun. But this kind of dispute is better left to experts..." It remains to be seen what rules he will follow in the future. I'll try to keep my eyes open.
But the point is that English singular they has been around for a long time. It is not new by any stretch. English has no gender neutral plural pronoun, so we speakers have long been faced with the challenge of "working around" our deficit.
I will act as conduit to my little piece of the blogosphere for Geoff Pullum's April 26, 2008 advice:
"Avoid singular they if you want to; nobody is making you use it. But don't ever think that it is new (it goes back to early English centuries ago), or that it is illogical (there is no logical conflict between being syntactically singular and semantically plural), or that it is ungrammatical (it is used by the finest writers who ever used English, writers who uncontroversially knew what they were doing)."
FYI: here's a sampling of various Language Log singular they posts going back four years, all of which seem to support Pullum's advice:
All posts tagged "singular they".
Facebook phases out singular "they" (Benjamin Zimmer, June 27, 2008)
Canadian Department of Justice: use "singular they" (Mark Liberman, April 13, 2008)
Lying feminist ideologues wreck English, says Yale prof (Geoffrey K. Pullum March 02, 2008)
Singular they on Facebook (Eric Bakovic, April 28, 2007)
"Singular they" mailbag (Mark Liberman, September 15, 2006)
"Singular they": God said it, I believe it, that settles it (Mark Liberman, September 13, 2006)
Is "singular they" verbally and plenarily inspired of God? (Mark Liberman, August 21, 2006)
They are a prophet (Geoffrey K. Pullum, October 21, 2004)