I went to see the Davinci Code yesterday and saw a preview for a movie called the Lakehouse (or something similar). The 'catch' for the movie is apparently a mailbox that lets the two people, who live in the house 2 years apart, send letters to each other (the woman puts a letter in, and it shows up 2 years ago in the mailbox for the man to get, and vice versa). Now, in the movie they apparently just use this thing for love letters. What would you do with a 2-year into the past mailbox? My first inclination would be to solve some computationally difficult problems (prize money for breaking RSA codes, anyone?), then I'd try to create paradoxes.