I'll have a column on this subject tomorrow at NRO, but there's no way (as usual) to say it better than Lileks (sorry, no permalink, he screwed up--maybe I can fix it later, but it's good through the end of Monday...):

...we're not sending smart toys on our behalf - we're sending human beings, and one of them will put his boot on the sand and bring the number of worlds we've visited to three. And when he plants the flag he will use flesh and sinew and blood and bone to drive it into the ground. His heartbeat will hammer in his ears; his mind will spin a kaleidoscopic medley of all the things he'd thought he'd think at this moment, and he'll grin: I had it wrong. I had no idea what it would truly be like. He'd imagined this moment as oddly private; he'd thought of himself, the red land, the flag in his hand, and he heard music, as though the moment would be fully scored when it happened. But there isn't any music; there's the sound of his breath and the thrum of his pulse. It seems like everyone who ever lived is standing behind him at the other end of a vast dark auditorium, waiting for the flag to stand on the ground of Mars. Then he will say something. He might stumble on a word or two, because he's only human.