I am trying to find an application that will let me add birthdays to a contact from my phone. I switched to an AOSP ROM for my DX, and I kind of miss the better contacts app that comes with stock DX. I know I can add the birthday from my PC, but doing it from my phone would be fantastic.
i add them to Google Contacts in each Contact's Birthday field. then on the Google Calendar you can select "Browse Calendars" and choose "Contacts' Birthdays" and they show up. also "U.S. Holidays" is a good one to add too. i've found that you must add them on the PC side and not on the Android side - otherwise - they won't show up.