Pin the Face on the Name

When you're reading a novel or short story, do you consciously cast someone based on the author's description of the character, or is the character more a nebulous "soul" in your mind? Does your imagination have a big central casting file (made up of friends, family and/or famous people??) and do you match descriptions to fit the actors who inhabit it, or do you just read and go with the flow.

I think I do a bit of both, but I tend to not have concrete, exact pictures of people in my head when reading about them.

I wonder .. what did Mr. Darcy look like before Colin Firth? What's Jack Reacher really look like? I've got a picture of him in my head, but (even if I had the artistic skills) couldn't draw a portrait of him (if Jason Stratham had a bigger brother he'd be a good casting choice). Are Dickens characters real in your head, or exagerrated cartoons/charicatures?

Tell me how you see people when you read. How "real" do they get? If you write, tell me what you try to get your readers to see.