Designers win, because they use one design (compliant, too!), for all browsers. Users win, because everyone sees the same design/version/look.
Best yet, when you pile on a library that fixes CSS3 (this article), and one to fix the CSS box model ( http://webdesign.about.com/od/css/a/aaboxmodelhack.htm ), and then another to fix the png transparency issue ( http://code.google.com/p/ie7-js/ ), and another to add canvas support ( http://excanvas.sourceforge.net/ ), and another
Then you explain that everyone will see the same design (yay!), and people using older browsers will experience a VERY SLOW page load. That is why they should upgrade to a more up to date browser.