Bad things will happen if you don't - so I will blatantly plagiarize from John Scalzi:
Also, as usual, John says exactly what I've thought about this whole election. Go read.
Election List X: Some of The Horrible Things That Will Happen To You If You Don’t Vote
1. Your penis will fall off. If you are a woman, you will grow a penis, which will then fall off.
2. Your peers will point and laugh at you more than they already do.
3. You will have to listen to smug voters say “if you didn’t vote, you can’t complain” for at least two years.
4. You will be consumed by pillbugs whilst you sleep. They will leave behind nothing but your penis, which as you’ll recall, has already fallen off.
5. You will smell of sour buttermilk until the next New Hampshire primary.
6. Uncontrolled flatulence.
7. Cars will swerve to hit you, even when you are inside your own home.
8. Your World of Warcraft party will turn on you and smite you mightily.
9. Impotence. And not just because your penis has fallen off.
10. Stairs will rise to trip you.
11. Boils. In Biblical plague amounts.
12. Static cling that no amount of Bounce sheets will ever cure.
13. Your cat will take a dump somewhere in the house that you will never find, and the smell will be carried through the air vents for months, all the while the cat will stare at you with that “you’re a real asshole” look they sometimes have. If you do not have a cat, one will be provided for you for the length of time required for it to crap in said undisclosed location.
14. Your credit card will be canceled and your creditors will send someone to repossess your penis. Which has fallen off.
15. Your favorite TV show will be canceled and every time you try to buy the last season on DVD, retailers will be out of stock.
16. Your children will disown you. If you have no children, you will be summarily adopted by a family, and when you attend Thanksgiving at their home, you will be told how disappointed they are in you. For six hours straight. After which they will disown you.
17. Your cabbies will henceforth always take the long route to any destination to which you travel.
18. Zombies, and you without a shotgun.
19. Everyone on your street will win the lottery. You will get a rock.
20. I swear to God, I will learn your address, come to your house, and when you open the door, I will totally kick you in the nads. Which will hurt even more because they’re the only reproductive organs you have left. Because your penis has fallen off.
I endorse Barack Obama for President of the United States and will be voting for him on Tuesday. I heartily encourage you to do so as well, if in fact you have not voted already.
I’m going to vote for him because I believe he is what I think a president should be: Smart, informed, engaged, practical in ideas and in the execution of those ideas, deliberative and as we have seen in this campaign, someone who keeps his head while all those around him are losing theirs.