ETI
Life elsewhere in the universe is probably pretty common. Certainly, the biochemistry that produced single-celled microbial life here on earth is at work in a myriad of locations throughout the universe.
But, I suspect intelligent life is really quite rare. A really good read on the subject is Rare Earth," by Peter Ward and Donald Brownlee (Copernicus Books, 2000). In it they explain why simple forms are life are probably quite common, but that its entirely possible we could be the only intelligent creatures in the universe. Makes one feel somewhat lonely.