When it comes to physical description in stories, I tend to go with the "less is more" approach. For secondary characters, I'll give a few defining features to help get the readers' imaginations going. But when it comes to main characters, I tend to avoid physical description all-together. Why? Well, as a reader, I like imagining characters any way I want to. So I guess this is my attempt to give my readers that same freedom.
Ironically, after all the time I spent not describing my main character in My Very UnFairy Tale Life, I then got a book cover that shows the main character front and center. I must say, though, that if I did have to have a photo of my main character on the cover, I'm glad it's a girl that looks a lot like what I was imagining.
Don't get me wrong: I have nothing against physical description. Sometimes it's quite necessary in order to convey something about the character. For example, I just finished reading Every Day by David Levithan (a fantastic book!) about a character who jumps from body to body on a daily basis. In that story, physical description is absolutely necessary in order to differentiate the various people the protagonist inhabits.
How about you? Do you like the freedom of imagining characters however you want, or do you prefer physical description to be more concrete?