I came across this survey of current and future computer usage from college students. SurveyU (http://www.surveyu.com/) is a survey research organization that has established a representative panel of college students within the United States who share their opinions on a wide range of issues, In a survey in Sept 2007 students were asked about their computing plans (http://www.surveyu.com/images/pdf/campus_computer_press_release_-_102207.pdf), the results I've put in the table below. Whilst the current global market share is around 7% it is apparent that usage amongst US college students is considerably higher with 23% using Macs. What is even more interesting is that 44% of students plan to purchase a Mac as their next purchase. Update: Appleinsider are now quoting a report from Student Monitor/Morgan Stanley suggesting 40% of college students plan to buy a Mac, unfortunately I can't find a link to the original source.

I did a quick search and I have compiled a table below giving details of published data, if anyone has links to further information I'd be delighted to add it, since it is often useful to have all the info in one place. Some of the links also have historical data and it is apparent that Mac usage has risen significantly over the last 5 years. Updated 17 April 2008 with data sent by readers.