Heya, I'm the one that took the photo =).
It's funny, when I first heard about the birthday celebration I thought it wasn't gonna be that good an idea (definately not matching the Year of a Million Dreams which I thought was really cool), and it'd be just another gimicky marketing campaign.
But boy it works! Every second group of people you see has someone wearing a birthday button! Disney really managed to pick a winner with this campaign.
I guess the downside is that with some many birthday-ers, the special treatment gets lost. I remember when I went to Walt Disney World for my sixteenth birthday, I got given free badges, stickers, a Star Wars trading card game, a Mickey spoon for my snow cone and a bunch of other stuff - oh, and a birthday phone call from Mickey (or was it Goofy). I'm guessing they don't have the time or the funds to do this anymore, which is a shame.
I've also tried to say happy birthday to all the badge wearers I see... but it gets too difficult lol! I said it to one woman once and she gave me the straaangest look as well >_<! You'd think she'd be more cheery if it was her birthday AND she was at Disneyland!!