Ask HN: Should my new website support IE 8 users?

The conventional wisdom is if 10% of your users are on a particular browser, you should probably support that browser. The problem, however, is that if you build an HTML5/CSS3 Responsive website from scratch you inevitably end up spending a great deal of time putting in hacks just to get things working somewhat similar in IE 8 (which doesn't support a large number of the new standards coming out now). To give an example, I spent over 5 hours yesterday working on a silly image overlay issue because of the weird way that IE 8 handles z-index. If you have the resources, of course it makes sense to build in some type of support for such a large number of users, but if you at a small startup where there is very little time for anything shouldn't you focus on the 90%? I know BaseCamp is doing this with their latest version, but is it crazy to force the use of alternative browsers? Is the huge effort needed to make things easy for that 10% worth it?