NEW YORK - In the year 2009, on the 25th of April, a man named Greg is supposed to get an e-mail. The e-mail will remind Greg that he is his best friend and worst enemy, that he once dated a woman named Michelle, and that he planned to major in computer science. "More importantly," the e-mail says, "are you wearing women's clothing?" The e-mail was sent by none other than Greg himself — through a Web site called FutureMe.org. The site is one of a handful that let people send e-mails to themselves and others years in the future....