Thanks that's interesting, I didn't realise so many sites were using it. I'm on a mac so I can't turn it on or off. Haven't used Internet Explorer in a long time and can't say I miss it. The only site which I have to use IE for is a banking one which displays fine in other browsers but has one form which won't work : )
Presumably the sites that I haven't noticed it on are serving up alternate content for other browsers. I wonder what they're using it for?