Identity theft is nothing new but from the recent articles on Facebook security holes (example) you'd think it was a whole new danger unleashed on the globe. The good thing about all the press it gets is that it is now mainstream thinking to be wary of putting any personal information on sites (wherever they are hosted – Facebook, Microsoft, Google, etc).
Thus, to reiterate, you should think very carefully about ever putting your birthday, home address, and any private interests online. You should assume that the site you are using WILL be hacked at some point. You should assume that people ARE trying to steal your identity. But you shouldn't get too paranoid and miss out on the benefits of sites.
As a matter of personal choice, I never put my real birth date on any site. I do however put my mobile phone number since I am trying to make myself as contactable as possible. I use a gmail or hotmail email address.
The warnings are good and useful, but balance is the key.