As of February 2009, scientists have counted 361 intelligent civilizations in our galaxy alone. There may be more also.
What we fail to guess is we firmly believe we are the only intelligent life and so, we only look for similar form life. Human eyes and other senses are very inferior. We can't hope to see and identify other forms of life that surround us and in the space.
Milky way Galaxy Image by Sir Mervs via Flickr
The discovery of more than 330 planets outside our solar system in recent years has helped refine the number of life forms that are likely to exist.