There should be a thing at the bottom of the forums saying "X users are celebrating a birthday" and have a list. It would just be a little recognition on your special day
I think it's a great idea. As long as it's optional.
And i don't really see how it is an invasion of privacy. It's just a birthday...
Also i think actually a lot of peoples birthdays are quite accurate, of course there are some people who for some strange reason lie, but other than that, it think it's fine.
I think it would be a nice thing to have. It allows us to connect to one another in a positive way. Though my only concern is that it would generate spam. As much as I like this idea, I don't want it to create extra spam. If there is a way to do it without spam coming with it, I'm all for it. Good thought!