Internet Explorer for Macintosh has been discontinued, and will no longer be distributed by Microsoft after January 2006.
Despite the best efforts of the browser industry to establish and conform to standardized technologies, the differences between various web browsers are sufficiently taxing that the builders of any web site have to make a business decision about which web browsers to support with their site's design. There are so many browsers out there, each with its own variance, that developers of a site can't possibly build for and test them all. A line is drawn, typically based on market share, but also based on target audience, as well as the biases and perceptions of the people making the decision. Some browsers just don't make the cut.
Browsers specific to a platform, such as the Macintosh-exclusive Safari browser, drag operating system perceptions and biases into the browser wars: Site builders acknowledge that a percentage of people in the world use Macs, but is it worth building for and testing a browser that's only used by 5% of the population, and possibly less of a percentage in our target audience? Some browsers, like Firefox, are seen as cross-platform solutions: If the site works in Firefox for PC, it should work in Firefox for Mac, therefore Mac users would be able to see the site with some browser, and so we do not need to support Safari. (Nevermind customer preference for a particular browser, or the inconvenience of opening a different application just to get to one particular web site.)
Experienced developers know that the cross-platform assumption couldn't be more false with regards to Internet Explorer for Mac, yet site builders with a strong Microsoft bias (typically those that use MS technology on the server side) still assume that IE, by far the most popular browser for Windows, is the only browser that needs to be supported, and Mac users can always use the Mac version. Some sites go as far as to block browsers that don't identify themselves as Internet Explorer from seeing anything on the site, even if the site would be reasonably functional in other browsers without changes.
FlexCar, I'm talking to you: Whatever MS-certified contractor you hired to build your site two years ago set up a blocking mechanism to prevent non-IE users from logging in to the reservation system, likely because he couldn't get his fancy time-range selector grid widget to work in other browsers, and/or because he convinced you it wasn't worth trying. I still contend that falling back to a simple table display for other browsers would be inexpensive and allow the rest of the world to use your service, but you seem to think the widget is more important, possibly justified by the existence of IE for Mac. Well, IE for Mac no longer exists. What are you going to do? Update: They're gonna make me feel stupid by building cross-browser support into their web site a long time ago without telling me, is what they're gonna do. Yay Flexcar!
The official death of IE for Mac tolls the bell loud and clear: No more excuses. Support standards-compliant web browsers.