Why Not IE?

Security

IE makes it incredibly easy to install malicious software on your sytem without you knowing about it, mostly through ActiveX. With one line of code (javascript) it is possible to crash IE6 and most versions of IE7.

Web Standards

IE does not follow the standards that modern browsers should be required to obey.

"The Internet works for one simple reason - everything at its core has been built on agreements that bind it together ... These agreements are forged by a body of people whose goal is nothing short of designing a better and more efficient Internet for everyone. Microsoft, for some odd reason, seems bent on breaking stride with these agreed-upon standards." -Tech News Watch