I used to vote in every single election (almost always for a 3rd party candidate!). But I can tell you from working on Cindy Sheehan's campaign for congress that the system is rigged. That was also the message of that movie about Harvey Milk, as I recall. He kept running for City Council, but it wasn't until they passed a law to de-rig the system (and create fair voting districts) that he was actually able to get elected.
It's time to step out of the box that's been so carefully crafted for the American people. Republicans? Democrats? That's not much of a choice. We've got the same puppet master running the puppet show and they would have us all mesmerized by watching the puppets bash each other in the face.