Gore has traveled around the world speaking on global climate change, and the movie contains part of his presentation and other scenes of his travels. Some of the information you might have heard before, however there is some info that Gore convinced the US military to release. For example, the military felt that the thickness of the ice sheets in the arctic should be classified for national security (the issue that the US has these records and not Canada is a sore point for Canada). As you can imagine the thickness of ice has declined since they started keeping records 50 years ago. The movie is a good summary of the body of evidence that the earth's climate is changing and we are involved.
Go see this An Inconvenient Truth, and take someone with you.
* in the movie and elsewhere people use the term Global Warming, I prefer using the term Global Climate Change since many things are happening besides an increase in temperatures. There are more cases of extreme weather, intense storms and droughts. Also with the term Global Climate change on a cool day - people don't say "I thought there was global warming, why do I have to wear a sweater in March."