I can say that IE 9 is unhappy with Elegance (we're running a beta install of 2.6.2). IE 10 and II seem OK. I haven't been tracking Firefox and Chrome through the versions, but I haven't found a version of either in my enterprise that struggled with it.
I will say that the boxy links don't degrade well when screen resolutions are set large, but that needs to go on a different thread...