Net Applications: Mac market share drops nearly 0.5% in April

I'm still working my way through the Net Applications data for April but I've already seen another interesting data point. According to the data, the Mac market share dropped by 0.47% in April, taking the Mac OS market share back to levels previously seen in Nov/Dec 07.

Note: Windows excluded from the above graphic for clarity.

Curiously, the Windows OS market share increased by 0.42% in April. According to Net Applications, Windows XP market share stands at 73.92% (up from 71.59% in March) while Windows Vista stands at 14.23% (up from 14.02% in March).

Is this a transient blip, or has Mac growth finally stalled? Only time will tell.

Thoughts?