So, it took a little while but Facebook has sent me a response regarding the privacy breach which meant users' dates of birth were being revealed:
Due to a technical glitch, some Facebook users' full dates of birth were temporarily exposed. We have resolved the problem, and we'd like to assure you that this information is now being displayed according to the privacy settings that you originally chose for it.
Please be assured that Facebook takes users' privacy very seriously. We regret this error and we apologize for any inconvenience it may have caused you. Let us know if you have any other questions or concerns.
Thanks for contacting Facebook,
Thanks for getting back to me Oliver. My own tests have confirmed that the problem no longer seems to present - which is obviously a good thing as dates of birth can be a useful "stepping stone" for criminals intent on identity theft.
There is a bigger issue here, however. Is user confidence being shaken in the ability of websites like Facebook to properly secure the data of its members?