I do that - Whenever I notice someone mentions when their birthday is (LJ stopped sending out reminders, I think. I've not gotten any of late, and I KNOW there have been birthdays), I make note. I have a file fulll of birthdays, anniversaries, addresses and phone numbers of you lot.
I watching youuuuu.
*cough* or I just realize I'd never remember otherwise.
Now to clean real quick before I call Jenn