MS is notorious for the "embrace and extend" methodology that marginalizes non-Windows OSes. The use of FrontPage extensions, IE proprietary tags, and the somewhat intentional handicapping of the Mac version of IE are only a few examples. Those who have championed standards here are correct.
Those of us who use Mac OS X are in many ways more fortunate than those who use Windows, because we can choose from an enormous variety of browsers, each one of which has its own specific strengths and weaknesses. OmniWeb renders pages beautifully but needs more work on its Javascript and CSS 2 implementations. Mozilla renders really fast but doesn't adhere to Mac's UI guidelines.
If Microsoft decides to let IE linger any longer it's going to fall further and further behind. OmniWeb in particular is repidly catching up to IE, and with the next version it has almost reached parity. My recent testing of OmniWeb 4.1 beta 2 has shown that it renders pages slightly faster than IE and its Javascript is really beginning to take shape. By the end of the year I believe it will be the best browser available for Mac OS X.
Frankly I don't care for Microsoft's browser deal with Apple. It's made them appear lazy. It would be total folly if they honestly think at this point that they don't need to stay competitive. Given their resources they could easily have created a browser with decent page rendering/caching speed and complete CSS2 support. Unless they have a secret IE6 in the works they're going to lose out to Mozilla, OmniWeb, and Opera in 2002.
As a side note, I work as a web developer. I refuse to use any tag, CSS property, or javascript method that isn't supported on Mac IE, Win IE, and Netscape. Often times this means I have to do a little extra works, but it's worth it to make my sites behave consistently for the widest variety of users. At present I'm trying to push our development group towards stronger adherence to XHTML, which is the purest hybrid of HTML 4 and XML. There are some voices of reason on the subject of standards, and here are my two faves:
Jeffrey Zeldman
http://www.zeldman.com
Jakob Nielsen
http://www.useit.com/alertbox/