This is an easy fix for the problem where the Birthday's calender (or other subscription cal like Holidays) is not being pushed to the iPhone or iPod Touch. 

From iCal on your Mac (not the .Mac or Mobile Me one)

Export the subscription cal you are wanting to sync. Import that calender back into iCal, it will import as a regular calender. Now delete the subscription cal you just imported/exported, or for the Birthday cal just uncheck it in the preferences/general menu.

Now when your Mac syncs with Mobile Me it will push the new calenders to your iPhone/iPod.

The only drawback to this is the birthday calender won't update automatically when you add a new contact/birthday, you will have to do this again or add them manually.