The sky isn't falling, the world isn't about to end, and PCs aren't dying. Why, then, is market research firm Gartner bugging out? Call it an overreaction or a temporary blip as tablets settle into the marketplace (or a little of both), but according to Gartner, worldwide PC shipments totaled 84.3 million units in the first quarter of 2011, a 1.1 percent slip from the same period one year ago. Doesn't sound like much, but Gartner says the shipment results are indicative of a potential sluggishness, not just a normal seasonal dip.