We all have various tools in our box to deal with the constant headache that is Internet Explorer. Browser hacks, conditional comments, filters, pounding our heads against the wall, etc (wait, is it possible that's where the headaches come from? I'll look into it and get back to you).
This situation gets even worse when one wants to use some of the fantastic techniques available to us in CSS3, like border radius, drop shadows, and gradients. In the past, we had to use images for all of these design elements, but now it's possible to have a fancy, shiny button that uses only a
<button> element and some css. Well, possible except in IE. Enter CSS3 PIE.