Just back from my sister's birthday party (which I'd totally forgotten a few days ago when someone suggested going to see Indiana Jones today, but fortunately I decided to stay at home and write anyway). While I was down there I happened to ask if one of my nieces (who hadn't made it to the party) had picked up her birthday present. Everyone said yes... then there was a long period of "I think she did..." as we got more and more confused about when she had last been round. Eventually we established that everyone was remembering her picking up the Xmas presents I'd left for her (which happened in March for various reasons) and that she hadn't actually been round since her birthday.
More cogitating about it, then we phoned and asked her and she said yes, she'd got the present. And phoned back a few minutes later and said no, she didn't think she had.
Eventually, to cut a long story short, we worked out that I never actually got the damn present - her birthday was the weekend after Eastercon and in all the rush of getting ready for the con, and being a bit ill afterwards, it simply slipped my mind.
So now I need to buy my niece a "sorry I missed your birthday" card and some vouchers. The silly thing is that if I hadn't asked we would have probably all assumed she had it, since I never usually forget birthdays. So it goes...