plastic versus paper

The city of San Francisco recently banned the use of plastic bags in grocery and convenience stores. Here's the story:

http://www.nytimes.com/2007/04/01/weekinreview/01basics.html

Is this a good thing? Maybe, although paper bags are not necessarily more environmentally-friendly than plastic. Paper bags take more energy and resources to produce than plastic bags. Plastic bags, however, last forever in landfills. There's not really a landfill shortage in the US and there never was, despite the worried cry of environmentalists during the 1980s. If we do a good job of recycling plastic bags (which we don't), are they really a problem?