Some great connecting the dots journalism from Jalopnik today. In 2010 Ford justified the end of the Mercury brand by explaining that "Of Ford Motor Company's 16% market share in the US, Mercury accounts for 0.8 percentage points, a level that has been flat or declining for the past several years."
The article goes on to point out that Lincoln's market share today is even worse than mercury's when it was ended. Lincoln currently enjoys a 0.57% market share in the US, and each year it seems to be going down.
Unless things turn around soon, Lincoln could join Mercury, Saturn and Pontiac in the car brand graveyard.