I made a bet with my girlfriend about something what I was totally sure in. The price was a Macbook Air - and I lost it.
I didn't have enough money but I wanted to keep my promise. So I gave her a Macbook for Christmas. She was very surprised when I gave her the great box, even when she started to open it and the other 3 boxes in it. After she couldn't believe that I really give her a laptop - until she checked it in more detail. Her reaction was unforgettable, and yes, absolutely positive.
Good idea for Christmas or birthday if you have too much spare time - I worked on it every single afternoon for 2 months.