From Brian Lindenmuth comes a link to a "Editor Roundtable: A Story Critique" where they've posted a short story that's been submitted and rejected by several markets. After you read the story you can read the explanations of eight editors as to why they explain what does and doesn't work about the story. There's some great insight into what's meant by editor preference. Some of the editors responding are: Ellen Datlow, Anne VanderMeer, and Gardneer Dozois.
The WonderBook site along with its sister site BookLife Now are great resources for writers learning the craft.