As I add more DHTML/AJAX to the sites I manage, I’ve been having more and more problems of IE6 locking hard when using the PNG alpha hack (either via straight Javascript or the popular HTC method). The locks happen only when someone’s browser does not already have the page loaded in their cache.
I finally threw up my hands this morning and removed all IE6 PNG workaround code from our web apps. That, of course, left the default background color around every icon in the interfaces, #D4E6EA. Solution? Changed the sites’ stylesheets to use that color for toolbar backgrounds, etc. No more locks or boxes, but now we have light cyan toolbars.
IE sucks.