Even setting aside that admittedly rickety fiscal argument, I’m not aware of any single piece of software that’s made Web designers unhappier than Internet Explorer. Most everyone I know just simply loathes it, and if they don’t, they lament the extra effort they need to expend in ensuring I.E. compatibility, time that could have been spent on positive endeavours.
Many of the hours I’ve spent wrangling with Internet Explorer were squarely unbillable, I admit, but it was my personal time that I was investing in making some side project work competently in I.E. It’s time that I should have been enjoying, not time I should have been spending gnashing my teeth together in frustration. Software cost can be quantified in dollars, but it should also be measured in human impact; its design matters.