As a matter of fact, for years Internet Explorer has slowed down the global development of web standards and, more broadly, the entire future of the web. For years web developers have been forced to, as Ian Hickson says, code to the lowest common denominator instead of coding to the standards. As a result, now many developers still use a small percentage of the full potential of web standards not because they don't know how to code properly, but because they're afraid of what consequences might result in Internet Explorer.
Do you really enjoy the practice of duplicating your code when you want to use XPath on Internet Explorer? Do you still like all the quirks, bugs, inconsistencies that come along with IE's implementation of web standards? That's quite masochistic, in my opinion. Instead, rethink the web in terms of new features that may be added now, today or in the future. Embrace the future, not the old, sinking relics of a bigon age when the e-mail was the only practical implementation of web communication.
In a nutshell: test in Internet Explorer, if this makes you feel relieved but code just as if IE doesn't exist.