Gliese 581g is the 6th planet in the Gliese 581 system located in the Libra constellation. Astronomers have determined 581g is neither too hot nor too cold for water to exist in liquid form, it also appears to have an atmosphere and gravity. All of these thing point to the possibility of sustaining life. This leads to two exciting possibilities, first life may have already developed there and second, it could be a possible location for colonization at some point in the future. Unfortunately we will probably not know either of these things for a very very long time. Gliese 581g is 120,000 billion miles away, considering at our current technological level it would take us theoretically 85 years (realistically more like 50,000 years) to reach our nearest neighbor, Alpha Centauri, a mere 4 light years away, traveling to Gliese 581g is WAY out of our league.
In my book this is pretty exciting stuff. Okay, I have excepted I will never get into space, the Challenger accident ended serious space exploration for a generation, we are only now recovering. However, this has never deterred me from dreaming the dream of every 8 year old boy of someday visiting another planet, I may never get there, but now I know there is a chance some distant decedent will someday walk on Gliese 581g and maybe even call it home.
Edit: I updated the travel times to Alpha Centauri