http://marketshare.hitslink.com/report.aspx?qprid=11&qpaf=&qpcustom=Linux&qpcustomb=0&qptimeframe=M&qpsp=136&qpnp=25

May, 2010 1.15%
April, 2012 0.98%

0.98 / 1.15 = 0.85

15%も減少