Differentiate

25-04-05_1650.jpg
Originally uploaded by Roostar.

I'm posting this - a picture of a colleague's mousemat - purely to shunt the horse head photograph down and off the page. It (the horse head) seems to have the effect of destroying the blog's shape when viewed on PCs with Internet Explorer. Mac's (with Safari) don't seem to affected the same way. If any of my English students are reading this, that was also an attempt to get 'effect' and 'affect' into a sentence. Or two.
Are educationalists the only people to use the word 'differentiate'?