On the Differences between Republicans and Democrats, and Why Voting in the Presidential Election Matters, by Science Fiction auther, John Shirley, via boingboing:
 

SOMETHING WICKED IN YOUR PERIPHERAL VISION...   Once many years ago when I was getting in trouble in a bad neighborhood in downtown LA, I told a cop who stopped me I was there to pick up my brother. "He uh--his car broke down and I came  out to help him but...he must've, like, gotten it started again and uh...I guess he left..."  I was sweating with the effort of maintaining so baldfaced a lie. I must have been highly, reekingly unconvincing, for he said to me, "You're so full of shit your glasses are steaming up."
I don't get in those situations any more. But I treasure that cop witticism and that is what I think of people who say that there's no reason to vote because there's no significant difference between Republicans and Democrats. They are so full of crap their glasses are steaming up. If they don't wear glasses, then the steam is pasting their hair to their forehead. If they don't have any hair then the steam is coming out their ears. They're full of crap, and furthermore they are utterly, gigantically wrong. There is a huge difference between the Republicans and the Democrats. They run the country differently, and you get different results. Sure, it's true that they both squirm in the hot tongs of special interests; they both have a tendency to try to please campaign contributors, and both sides are capable of corruption and oily prevarication. But they still have strikingly different policies. They appoint different people, who have different attitudes, and they give those people different directions on what to do in their jobs.
Look, if all the votes had been counted and Al Gore were President now, the air would be measurably cleaner than under Bush.  George W. Bush's EPA has looked for every possible opportunity to ease restrictions on air pollution. Gore would have reined in the energy producers and factories who are dumping mercury and other toxins in the air. Bush doesn't. People die from air pollution--people with emphysema, people with asthma, people with heart disease. Other people in the long term. But even in the short term, by the time the Bush presidency is done it's not unreasonable to assume that, because of Bush environmental policies, there are people who will die, and quite a number of them, who would NOT have died if Gore had been elected. (I know--I'll get to Iraq in a minute.) I'm talking about people suffering from air and water pollution allowed by Bush; I'm talking about --just as one example--children exposed to herbicides that Bush's people allow that Gore's people wouldn't allow: herbicides in soccer fields and parks and schoolyards and lawns can have extremely nasty effects on children. Brain damage, cancer. Even Bush's EPA has admitted this recently--but they don't do anything about it because the big chemicals companies don't want them to.
Bush allows lots of these sorts of things; Gore wouldn't have. Gore would not have opened every possible door for outsourcing jobs, either. I believe there are hundreds of thousands of people, at least, who would have jobs now if Gore were President--people who don't have them now because Bush is President instead. There will be measurably more wilderness preserved under a Democratic president. Millions of acres will not be clearcut under a Democratic president. Because Bush is in with the NRA lobby, there will be more guns on the street, more automatic weapons in use in the ghetto, than if Gore were President. Even if the difference is only say 25% fewer guns, that's going to save at least some lives. Gore would have worked harder to save social programs, decent school lunches, more school books; if you have a Democrat in office and you're living in a poor neighborhood, there's a better chance your kid is going to have the books and equipment and teachers he needs.
And Gore would not be looking to spend hundreds of BILLIONS of dollars in Iraq. He'd have found some other way to deal with Saddam.  And there are near a thousand US soldiers and thousands of Iraqi civilians who would now be alive if Gore had been elected.
So now you've got a choice between Bush and Kerry. They are very different. Kerry's no golden angel, and he's maybe not as inspiring as John Kennedy or as salt-of-the-earth as Truman. But he's going to appoint different people than George Bush would. He will not make foreign policy based on extremist religious notions whispered into his ears by the evangelical crowd: the Christian Coalition will not puppet Kerry. He will not get us into a war because it fulfills prophecy. He will not let the polluters do just anything they want and he'll try to find ways to keep jobs in America. He will help stem-cell research along  which just might save your life someday. In all those ways he's different from Bush.
Hell, if you're of draft age, you're more likely to be drafted if Bush is elected. Because you know they're going to spring that on us after the election.
It matters who you vote for.  And it matters if you don't vote. I mean, yeah, I'd like to have a more inspiring, more radical president than Kerry. But no one else desirable can be elected, this year. That leaves us with Bush and Kerry. And the choice between Bush and Kerry  has real, concrete, definite, measurable consequences--for your life and the lives of people you care about.