Listening to "statistics" from people who quote percentages is really dangerous.
Percentages are really, really, easy to lie with. And for people who only quote percentages, this is usually what they are trying to do. Spin.
You need both. Percentages are better for showing movement (e.g. growth), while absolute numbers give context.
Apple had 14% of the US retail PC market in Feb. 2008 -
http://www.appleinsider.com/articles/08/03/17/apple_snags_14...
This article claims the number was 8.7% in the 2nd quarter of 2009 -
http://www.appleinsider.com/articles/09/07/15/single_digit_g...
According to this article on theappleblog.com, Apple has 4% of the global PC market as of July 2009 -
http://theappleblog.com/2009/07/25/does-apple-have-a-91-perc...
If anyone has more, I'd be very curious to see them (especially the ratio of sub-$1000 retail PC sales to $1000+ retail PC sales).