I tell this to startups all the time. You need to test your sites and products against IE, even if that isn’t your preferred browser. CNET posted a story today that shows the increasing usage of IE on the desktop. You can check out the story here:
Internet Explorer resumed growth in browser usage in March, reversing a years-long slide at least for now. IE9 in particular grew fast, but Microsoft is weak in mobile browsing.
One of the easiest ways to test against IE is to use the Internet Explorer Application Compatibility VPC Images available from the Microsoft Download Center. To use these, just set up a Windows 7 machine with Virtual PC and use the images here for testing:
In order to help web designers and web developers test their websites in older versions of Internet Explorer, we've provided the following VHD with Windows set up with the specified version of Internet Explorer. The images are patched with the latest security updates and are otherwise clean installs of the operating system with very few modifications.
These images will allow you to test your sites and apps against IE7, IE8, IE9, and even IE6 on Windows XP.
Setting these up is pretty easy. I would be glad to do a video if anybody wants to see how this looks on the PC.