Renders pages incorrectly. Web designers then need to spend extra time working so that pages work in Internet Explorer. This puts costs up, and slows the web down.
Doesn't let people resize certain text sizes. This means those with poor sight cannot read small text on many sites.
Far slower program than other web browsers
Far larger program than other web browsers
Isn't as user-centric as other web browsers. It lacks many handy features such as tabbed browsing and integrated search