Do you believe that outer space aliens have visited us or that they walk among us?

I have a buddy I grew up with that believes that space aliens have visited Earth. I will not go into the convoluted logic that allows him to come to this conclusion. It is sort of like people who believe there is a God. He has simply decided that it is true. I love the dude, but there is no arguing with him about space aliens.
But a whole lot of people on Earth believe in God.
So I figure the same logical progression would lead at least some of them to believe that space aliens had visited or where actually here.
I would like to know if any Flutherites believe that space aliens have checked us out, or if they are actually here.
Do you think so?
Why do you think so?