Happy birthday! I'm lousy at remembering birthdays; I think, of all of my friends, there are only four I remember consistently besides my own (and two of them are because they're on days that are memorable for other reasons).

As an adult, for me, birthdays have been "holidays" that I celebrate *with* friends, rather than the holiday that one's friends should always remember. It's my day to do whatever I want (though I don't take off work on that day). So if someone forgets my birthday, I'm not offended, and if they remember it, I'm pleasantly surprised.