I have the same problem. Just bought my Samsung Galaxy III and after adding my email accounts, my birthdays were duplicated in my calendar. I cleared the calendar, removed my Gmail account and then readded Gmail account. Now, I have no contact birthday's in my calendar -- and yes, my contacts on my phone (and in Gmail) have birthdays assigned to them.
When I try to sync my calendar with Gmail -- thinking the birthdays would come from there instead of my phone contacts - I receive the error "sync is currently experiencing problems it will be back shortly".
I just want my birthdays in my calendar -- sure it would be nice to have my Cloud calendar or Gmail calendar also, but want to start with birthdays.
Thanks,