Back in 2007, it looked like the state of California might follow San Francisco's lead in banning "disposable" plastic bags. The "why" question of worrying about plastic bags comes with the problems that they have during their persistence in the environment:
However, we received news today that California senators decided to nix the whole plan that could have prevented tons of plastic waste sitting in a landfill or finding its way into the ocean, citing that it would be too costly to consumers. Maybe I'm a little cynical, but whenever I hear people citing "too costly for consumers," I'm immediately wary of the real motivations of the person saying it, especially when I am not convinced of their arguments.
Still, on the same day (well, on the next day, since American Samoa is on the other side of the date line), we hear that American Samoa has decided to ban the use of disposable plastic bags on the island. Go territory! Of course, living on an island in the Pacific Ocean, one is very aware of the problems of limited space, especially with regard to all the problems inherent with imported plastic bags that end up in landfills and the surrounding ocean.
On another note, there is also the really artistic film on the life of a disposable plastic bag: