If you have birthdays stored in your contacts and would like to see reminders in your calendar, then you can use this little form to convert your Google Contacts to a calendar ICS file.
How to use:
Go to your Google Contacts Page, click on Export on the left.Select your desired contacts and Google CSV as type and hit Export.
After converting you can simply create a new Google Calendar (or whatever Calendar you prefer) and import the generated birthday_calendar.ics file into it.
Disclaimer: Your data is only stored for the convertion on the server, then immediately deleted.