I don't care if anyone knows how old I am, but I do have an issue with putting my birth date out on a public site for identity theft reasons. That is just one piece of information that makes it easier for someone to get access to your credit, medical, employment, etc. records.
I am very careful regarding sharing my personal information on the internet, and I won't put my birth date (even w/o a year) on any site -- facebook, myspace, forums, etc. It is just not worth the risk to me.
I just made the post to inform people that they are putting their birth date on a public site by posting their number here, in case they didn't realize it. It doen't bother me a bit if you want to share your information to the world.
Kurt