I also have to rebut rufnek's idea that Casablanca was a B-movie. It may have been bought and considered a B-movie when Ronald Reagan was attached to the project, but Bogart, fresh from the Oscar-nominated The Maltese Falcon, bigtime, imported star Ingrid Bergman, and A-director Michael Curtiz, who had directed many of Warner Bros. highest-grossing films in the previous 10 years, definitely proves that when the film was shot it was meant to be a class production. Now, whether they thought it was award-worthy is another story. The script kept changing on a daily basis. Even so, when Holden says it has 30 memorable, quotable lines, he's lowballing it by half!
Maybe Curtiz was handpicked to direct the film because of his money-making reputation, but there also are lots of stories from the Big Studio days about award-winning, high-grossing directors often being handed a B-film by a producer simply because that director was available at the time and under contract to the studio to deliver a certain number of films within a certain period. As for Bergman, was she was really imported specifically for that film? If so, that would certainly indicate some sort of special push for that movie, but the way I heard it, there was more happenstance involved. But then that could just be urban legend. I dunno.