I was driving baby girl to my parent's this morning as I do most Tuesdays thinking, "Wow, I'm going to make good time today."  About 15 minutes from their house (after driving about half an hour) I realized, "Wait a sec, my Dad is unable to take care of baby girl today I think."
I pulled into a supermarket plaza and parked the car.  I called my Dad to confirm and indeed today is the day that he's unable to take care of her because of a prior commitment.  It was then after hanging up the phone I felt like saying, "F*ck!", or "Shit!", but it wouldn't coincide with the melody of the kids' CD that was playing.  It was at this point I was debating whether to just bring baby girl with me to work.  Then I thought better of it.  Try keeping a 2 year old in a cubicle for eight hours without fuss.  I don't think it's possible.
After making calls to my wife and my mother-in-law to make sure it's ok to drop baby girl off with her, I turned around and back-tracked home, enduring another go around of the medley of songs on the kids' CD.  After dropping her off at my in-laws, I trekked back toward work, but by this time traffic was lighter so it wasn't so bad.
Moral of the story:  Write stuff down as you get older.