I know the portion of IE6 on the web is still around 25%.. but do you know what portion of your customers is actually using IE6 still? I wonder at what point i

I know the portion of IE6 on the web is still around 25%.. but do you know what portion of your customers is actually using IE6 still? I wonder at what point it is justified to return a 'please update your browser, preferrably to one of these: [list of reasonable browsers]', just because of the effort it takes you to keep IE6 compatibility.