Before Kepler, astronomers had found a little more than 500 exoplanets. Thus far, Kepler has found 1,235 candidates, more then double the amount humanity has ever found. These need to be individually confirmed, which is a slow process. Out of those 1,235, 15 have been confirmed as planets. It will take quite a bit of time to cross check the remaining 1,220 candidates, but the current findings have left researchers quite excited.
Before Kepler came online, only massive planets many times the size of Jupiter could be detected, and these were often only found because their orbit was very close to their star causing a noticeable wobble. Recently occulting techniques have been employed to detect planets, but the going was quite slow. But with Kepler's more refined telescope, it is able to detect much smaller plants passing in front of the stars. Among the many candidates found, 68 of them are believed to be Earth sized. With an extended estimate based on the current data, this places Earth like planets being found around 6% of stars. Even more intriguing is that 54 of the candidates were found to have an orbit within their stars habitable zone, the region around a star where liquid water is able to form.
There was much hope that some planets would be found that are both Earth like in size (125% the mass of Earth or less) and within the habitable zone. Kepler did find such candidates, 5 of them in fact. From these numbers, the Senior Astronomer for the SETI Institute, Seth Shostack, estimated this:
"Within a thousand light-years of Earth" there are "at least 30,000 of these habitable worlds."
This already shows that our galaxy has far more planets then was was suspected. It also shows that our galaxy may very well be filled with planets that life could develop on.
Seth Shostack, A Bucket Full of Worlds