Internet Explorer is that it does not comply with standards. This problem is compounded by the fact that a significant group of people use it. The excuse that Microsoft used was that Windows and consequently Internet Explorer was used by everybody anyway.
The problem is that this is no longer the case. With the advent of browsers like Firefox, Chrome and Opera there are superior product available that do support the open standards that make for an Internet that is no longer dominated by cripple ware.
The fundraiser of the Wikimedia Foundation, the development of LiquidThreads, all have to deal with the vagaries of the different incarnations of Internet Explorer. It is problematic when you read that developers are looking for a license. The biggest problem is for Microsoft; as developers do not have their Internet Explorer anymore they expose the myth that IE will continue to be able to get away with broken implementations of standards.