Apple caught the PC industry off-guard in June when the company delivered the MacBook Pro with Retina Display. The four-megapixel LCD renders text and graphics with extreme clarity, and most who saw the display came away impressed. But Apple may not be the only kid on the high-pixe-density block for much longer. Acer plans to include Retina-class displays in several laptop models, including at least one Ultrabook, by late spring.