Yeah, I'd probably restart just so I could go, "they're going to fly jets into the World Trade Center! Also, Oklahoma City is going to be bombed at some point! And the Unibomber is Ted Kacynski! And don't vote for Bush!" I probably wouldn't be listened to, but I would forever be known as the 13 year old who predicted 9/11. Hmm. I'd also put more effort into getting to know certain girls in school and being more openly funny. If I had known just how little junior high school mattered, there would be a couple bullies with some unpleasant memories of times they got their asses beat.
A girl I had a huge crush on is now happily married to a guy she met in college. Would it be unethical to try to steer her to me in the past, in essence crushing her hopes and dreams, but probably making my life a zillion times better? I know the name of her future husband, I know where and how she will meet him, and I know they'll be happy together. However, I also know enough about her now to know how attainable she was in high school, her likes and dislikes, and her overall personality. I'm not sure what I would do in that situation. Maybe try to be a friend? It's a very Back To The Future situation in which she was seriously injured and fell in love while being nursed back to health. Should I let that happen, too?
And record a couple of Justin Bieber songs. And invest heavily in Apple Computers (or get my parents to do so). Maybe get in on the internet stock bubble early and get out early.