Hi charris1980,
The issue with re-using data in users' MySites is that each MySite is a separate Site Collection. Data in Sharepoint does not roll up across different site collections, just across the same site collection. This is a great idea though. If you have this data somewhere in a form in a Sharepoint list (library), you could create a simple Sharepoint workflow to send the birthdate data into a calendar. There also may be third party programs that will do this very thing. You can check on Codeplex.com for some free add ons. I also know that Bamboo Solutions has a good list roll-up for across site collections. Good luck!