HTML, CSS, Javascript and more
Since IE8 you can force an IE8+ browser to handle a website like it is an IE7 or an IE8 browser. IE9 seems to emulate older browsers well, but I know at least one rendering bug and I’m wondering if some backwards compatibility bugs are overlooked.
A few new and cool CSS3 styles become realistic options when building a website if you combine them with IE’s filter.
If you’re accustomed to make websites by following the W3C guidelines, you’ll be suprised what you can’t do in IE when you have to work on a site that runs in IE’s Quirks Mode (at least I was).