Apple's Mac OS's share of the overall operating system market hit 8% at the end of 2007
This share is very likely to increase because of faster growth in Mac sales and because of the shift to laptops where Apple is even stronger with 17.6%.
Industry analysts predict that notebooks sales will exceed desktop sales for the first time in 2008. By 2011, IDC expects laptops to represent 66 percent of corporate purchases, with 71 percent of consumers opting for a notebook instead of a tower.
According to NPD, Apple’s U.S. retail notebook market share for June 2007 was 17.6 percent, an increase of 2.2 percentage points over the same period last year when Apple posted a 15.4 percent market share.
Apple has a 29% share of the premium notebook market
Apple has a choice in strategy to keep prices relatively high and possibly not hold market share gains or to get slightly more competitive in price and possibly allow sales of the Mac OS onto say Dell machines. Dell has indicated that it would sell and install the Mac OS if it was licensed by Apple.
The Inquirer made the case for licensing to Dell back in Jan 2007
The laptop shift and licensing to Dell could see Apple getting up to 40% operating system market share in 2011.