Cross Browser Compatible Wp Themes Development

Based on my own research, cross browser compatibility seems to be the thorn that is in every web designer’s side. Taking a mock up design and coding it to look the way it’s meant to be in all browsers at times, seems like an impossible task. I know when I’ve developed WordPress themes, getting them to appear correctly in both IE 7 and FireFox 2+ was such a pain, I would end up going for the (good enough) approach.