Many of the large insurance companies still hit my corporate site with IE6.
Mostly they should have been used to web not working properly. Also it's obvious that they do not care or are unable to install better browser.
What percentage of those 4% who use IE6 actually buy something? Is it worth supporting them? Or you could create an awesome site to sell your stuff more easily.
Don't bother getting animations to work in IE6, but make sure your site runs okay without them. The latter is doable.
If you have a website that does something useful for its users (and not just making a big, splashy presentation of the wonders of you) I like the idea of having a very stripped down fallback version with nothing but functionality that can be used on browsers with no CSS or Javascript at all. Sometimes even those of us who build websites and spend our days in dev versions of Firefox and Chrome have to use an obsolete browser to get some work done.
The downside is that most of the CSS work is done by javascript and if you are one of those IE8 users you will be unsatisfied with the pageload speed, but given the bad architecture of IE8 you will not be surprised by that fact. Although the pages using those polyfills work pretty good.
[1] https://code.google.com/p/html5shiv/ [2] http://selectivizr.com/ [3] https://github.com/scottjehl/Respond [4] https://code.google.com/p/css3-mediaqueries-js/
Now if you work for a businesses that only allow IE broswers then good luck.
Unless you are targeting a fairly specific type of corporate user/customer you probably want to consider adding some of the new jazzy client side stuff if you think it can improve conversions.