Feel guilty about the Everest like mounds of paper on your desk? Don't. They're an essential part of the human thought process, according to one research team. In a series of studies across many occupations, social scientists Abigail Sellen and Richard Harper, co-authors of The Myth of the Paperless Office, observed that when people read at work, they use annotating, cross-referencing and paper-sorting to tackle complex problems. When only electronic files were used, or when papers were filed away, workers weren't as effective. Piles of paper, they say, serve as "temporary holding patters" for ideas in progress. "People with messy desks don't have messy heads," says Harper. "Quite the contrary -- they've taken the mess out of their heads and piled it on their desks." So the next time someone comments on your state of disarray, tell them you're a stacker, not a slacker.