I'm confused! New birthdays that I enter in my Lion Address Book don't get synced with either my MobileMe account calendar online or my Mac's Calendar app.
Old birthdays (entered under pre-Lion OS versions) are still present in both situations. If I activate the Birthdays calendar within the Calendar app then the new entries appear, but I then have duplicates of all the older entries i.e. one appearing from the Calendar calendar, one from Birthdays if you see what I mean.