Two research firms say that Apple's share of U.S. computer sales shot up by 30 to 40 percent in the second quarter of 2008 over the same quarter in 2007. IDC and Gartner say PC sales worldwide rose from 62 to 71 million systems year over year, and Apple's sales increased in every market, even as the overall price-per-computer dropped.

The research firms said Apple sold 38 percent (Gartner) or 32 percent (IDC) more computers compared year over year, pushing it either into a clear third place after Dell and HP (Gartner), or tied for third with Acer (IDC), which acquired Gateway and Packard Bell in the intervening period. Worldwide, HP takes the top spot in overall market share, followed by Dell, Acer, Lenovo, and Toshiba.

Given that Apple typically keeps its price points about the same, improving features or reducing the cost of high-end add-ons - like the MacBook Air's solid-state drive, now $500 cheaper than at its introduction - this likely means Apple's revenue is higher than indicated by its roughly 8 percent estimated market share in the United States. According to Gartner, other firms are cutting prices steeply, trading market share for revenues.