It becomes a nice combination to have your Google contacts Birthday's listed in your Google Calendar.
Here is an useful link that describes how to integrate your Google Contact's Birthday with Calendar and how to set reminders for that.
Google has recently added a birthday field in Google Contacts and many people asked for an integration with Google Calendar. Creating a birthday calendar shouldn't be very difficult: Google created one for orkut friends, even if the calendar has a lot of limitations.
Until Google adds this feature to Google Calendar, you can try a third-party application that generates a public calendar for the birthdays associated with your contacts. The application uses Google App Engine and Google Contacts API, so your password is safe. Another good thing is that the calendar is updated automatically when you add new birthdays or you edit the existing ones. Add notifications if you want to receive an email or an SMS one day before each birthday.
The major downside is that the calendar generated by the service is public, so anyone who knows its URL can see it. To use the service, you need to grant it access to your address book...
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