The fact that we've found a habitable planet candidate so soon after starting our search has important implications for the number of habitable planets that may exist in our galaxy - which was estimated to be around 10 billion.
Having found Gliese 581g so soon though, may mean one of two things. Either we were very lucky, or there are more planets out there than we thought. Based on this discovery, it's possible that we may have many more habitable planets than originally thought.
Perhaps 20 to 30 billion stars in our galaxy may have conditions suitable for life.