Please be aware that the data does not mean that Apple's market share is 48 percent, the number refer to percent increase.  The data used in this post has been obtained from market research firm Net Applications (Market Share).  The total Mac OS X market share percentage checks in at 6.22 percent for January 2007.  Net Application's data allows the following metrics to be calculated:

Percent Increases

• Up 47.7 percent since January 2006
• Up 82.4 percent since January 2005
• Up 76.7 percent since April 2005 (Mac OS X Tiger launched April 29, 2005)

The January 2007 data shows an acceleration in the year-over-year growth versus the three most recent month (the number in parenthesis is the year-over-year growth for the respective month):

• December 2006 (30 percent)
• November 2006 (31 percent)
• October 2006 (35 percent)

In fact, the January 2007 year-over-year growth outpaced the 23.5 year-over-year growth seen in Janauary 2006.  The data clearly shows that the Mac user base is increasing.  The following is a view of Apple's Mac OS market share month by month for calender year 2007.  Note that Net Applications splits Mac operating system data into two groups, Mac OS and MacIntel.  MacIntel represents Intel builds of the Mac OS X operating system.  The January 2007 data can be found here.

Observe that Mac OS is shown to have 4.34 percent operating system share while MacIntel is reported to have 1.88 percent market share.  (Internet Explorer users may have difficulty viewing the images.  If so, click 1, 2, 3).  You can click on each image to get a larger view: 

2006 Data
Here's an overview of how Mac OS X grew during calender year 2006 (data provided by Net Applications) 

Mac OS X Intel Posts 23.7 Percent Increase In One Month
The data shows that Mac OS X Intel experienced a 23.7 percent increase as it's share rose from 1.52 percent in December 2006 to 1.88 percent in January 2007.  This outpaced the 17.8 percent increase from November 2006 to December 2006.