Celebrate pet birthdays?

I have always celebrated the birthday of my pets. I think this is mainly because I see my pets as part of the family, and it's also really cute to see how they react when you give them a present, and to record them trying to open it. Of course this only really applies to dogs and cats. I can't really imagine a gerbil trying to open a present! I think it's important though to celebrate a pets birthday, at least for me because like I said, a pet is part of the family to me.