Very very big universe and we have only studied a very very small percentage of it, smaller than 0.000*1%. However I think intelligent life is quite rare when you think that we have nearly been obliterated by so many natural disasters, asteroids, radiation etc and that isn't talking about man made inventions like the atom bomb. So the chance of intelligent life being as lucky and getting away with as much as us is slim. Though with innumerable amount of stars (more stars than there are grains of sand on the whole planet) it wouldn't surprise me if there were millions of intelligent species out there, however that doesn't mean the species are evenly distributed throughout the universe, we might be the only intelligence in our galaxy but other galaxies might have thousands...we just don't know.
Either way I think being alone would be quite a bummer wouldn't it? as the romanticist in me think that meeting Aliens could be one of the best things that could happen to us. All our religious, ideological and political differences would seem very very small and meeting them could unify humans in a way we haven't been unified before.
So yes I do think there are Aliens out there whether as microbes or just normal animals, and I do think there are intelligent Aliens out there. As for whether they are actually here abducting people and flying through our skies with big strobing lights? I doubt it. UFO's are a nice convenient coverup for governments testing new aircraft, a coverup made by the public and kept well fed by the public. The government just needs to issue periodic denials for the public who naturally distrust any authority figure to stoke the flames.
It's kind of on a bigger scale to immigration. The more people moan about immigrants stealing nationally born peoples jobs, the more the government denies it and the more people therefore start believing it.
It's all very
http://www.youtube.com/watch?v=Q2fGl9587X8