The only time I consider someone throwing away their vote is when they vote for someone that doesn't stand for what they believe in. If you believe in what the liberal Democrats believe in vote for them, if you believe in what the "compassionate conservative" Republicans believe in vote for them, if you believe in the US Constitution, then vote for the candidate who will honor, protect and defend the US Constitution regardless of his/her party affiliation.
Both partisan Republicans and partisan Democrats have gotten so hungry for power, they have forgotten the US Constitution and the reasons why they are supposed to be in power.