A recent study interviewed HR managers at a number of different companies, asking them how neatness of an employee's desk affects their perception of that person's professionalism. 65% said it "somewhat affects it", while 18% said it "greatly affects it", with only 17% saying it has no effect.
It isn't exactly fair, but it's something to think about when you're staring at your tornado of an office: you might want to tidy it up, if only to improve your reputation with your superiors.