Based on the data, the following observations can be made:

Percent Increases

The 38 percent year-over-year increase for April 2007 continues to demonstrate a slowdown in the year-over-year growth since February 2007.  You can see the declines in the chart below in green.  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 April 2007 data can be viewed here.

Observe that Mac OS comes in at 3.89 percent operating system share a decline from the 3.94 percent in March while MacIntel has risen to 2.32 percent, up from March's 2.14 percent.  The April 2007 Mac OS data, representing PowerPC builds of Mac OS X continue to follow the declines first seen in the February 2007 data as April demonstrated a 1.3 percent decline.  You can click on each image for an independent view:

Mac OS X Intel Posts 8.4 Percent Increase from March 2007
Net Applications' data demonstrates that Mac OS X Intel experienced a 8.4 percent increase from the prior month as it's market share rose from 2.14 percent to 2.32 percent.  The increase was well above the 2.4 increase from the preceding month.



Commentary
Although below the February and January numbers, April marked the return to operating system market share growth reversing the decline observed during March 2007.

About Market Share
The following is taken from the Net Applications site:
"This data provides valuable insight into significant trends for internet usage.  These statistics include monthly information on key statistics such as browser trends (e.g. Internet Explorer vs. Firefox market share), search engine referral data (e.g. Yahoo vs. MSN vs. Google traffic market share) and operating system share.

We use a unique methodology for collecting this data.  We collect data from the browsers of site visitors to our exclusive on demand network of small to medium enterprise live stats customers.  The sample size for these sites is more than 40,000 urls and growing.  The information published is an aggregate of the data from this network of hosted website statistics.  The site unique visitor and referral information is summarized on a monthly basis"