The big two parties have a vested interest in the big lie that voting for a 3rd party ‘wastes’ your vote. In fact, your vote will have the BIGGEST impact if you vote for a 3rd party. If Ralph Nader or Harry Browne could get 5% of the popular vote, that would create a special interest group big enough for the major parties to pander to, which would help move government in the direction you want it to go.
So if you are generally for less government, you’ll do a lot more good voting for Harry Browne than for George Bush. Harry’s not going to get elected, so you don’t have to worry about some of his more extreme positions, or what kind of leader he’d be, or any other ‘practical’ concerns. What you can use him for is a conduit to get your message through to the people in charge.
The same goes for Nader. If environmental issues are important to you, but you won’t vote for Nader because of some specific reason, you’re still better off voting for him than for Gore, because a vote for Nader indicates a preference for a direction you want the government to move in.
A vote for Gore or Bush indicates that you are happy with the status Quo. If that’s the case, great. But if you want the government to move, push it from the fringes where you’ll have the greatest effect.