Billyuns and billyuns..
No, seriously, my guess is that's it's pretty likely that microbial life exists in many many extraterrestrial locations. Of those worlds, some fraction have given rise to civilizations (although we will always have Madonna). If you enjoy skating way out onto thin ice, read this interview with Dr. Michio Kaku, about the next Copernican revolution.
Update: The perspective of an alien when visiting Earth.