From the release:

The Washington Post and The Baltimore Sun today announced that effective January 1, 2009 they will share selected stories, photos and news content with each other in order to better serve readers of both newspapers.

The Post and The Sun have agreed to share the newspapers' day-to-day
coverage of certain Maryland news and sports. In addition, The Post and The Sun may draw on each other's national, international and feature stories that are distributed by the LAT-WP News Service, to which both contribute. The exchanges will allow each paper to take advantage of the other's strengths and expertise in specific subjects around the region and the world. ...

As part of this accord, exclusive stories will not usually be shared, nor will coverage of such competitive subjects as Maryland state government and University of Maryland athletics.

The real question here is: What threats are both the BaltSun and WaPo trying to stave off? Increased competition on metro stories? A way to fill the pages without filling the payrolls? Readers, let us know your thoughts...