I love CSS3PIE. I love that I can make use of some of the CSS3 niceties like rounded corners and box shadow, and even IE7 and IE8 can keep up with the more modern browsers and not look too shabby. But if you're adding or moving elements around on your page dynamically, e.g. changing something from display:block to display:none and back, sometimes PIE can't keep up and leaves a box shadow in a strange place.