First I heard of it was when my daughter came home from school today all disappointed that she'd forgotten to wear purple. She says she's right in there next year!
I thought it was just something her school was doing - I didn't realize it was bigger than that until I saw this thread.
And FWIW - I don't think the "I won't wear purple because bullying hurts everyone not just gays" argument holds water. Well, not unless those same people would also refuse to wear pink ribbons for breast cancer awareness (after all, cancer hurts lots more body parts than just breasts), or red on Fridays to support our troops (what about civilian employees of the military?), or any other sort of "awareness" campaign. If they opt out of them all, then I can understand. Some people just aren't joiners.
Me, I would have worn purple, if I'd known.