Well, you'd have to be kind of dumb to say that there are no other intelligent life forms in our galaxy alone, muchwise the rest of the universe. Look at Drake's Equation; something definitely exists. As far as Roswell, I'm not too sure. If an extraterrestrial craft did crash, and a being was recovered, the government definitely wouldn't tell the populous. Shit would go down, and people would probably die over it. I would love to know if it was a creature, but I also respect that the government is a pretty intelligent group of people. I'm sure their cost-benefit analysis yielded that it would be best not to tell us if it did happen.
I personally believe that E.Ts do exist, and that they have definitely visited Earth. There's too much pointless attention that's been drawn to them. Ridiculously elaborate crop circles, and such. I think we'll find out eventually. And if the world does end in 2012, I hope it's by some sort of intelligent alien life. That would be a cool way to die.