I noticed IE drop below 50% last spring on http://flashcarddb.com
It dropped from 50.17% in March to 49.05% in April, continuing to steadily decrease since then.
My traffic is about 70% North American. I have many students. Macintosh is a 20% slice of my OS pie and Safari isn't too far behind Firefox in browser share.
September => IE: 48%, Firefox: 24%, Safari: 16%, Chrome: 10%