Apple had a WWDC 2012 session on optimizing web sites for high DPI displays. Interesting but not terribly complex stuff. I think if you follow the best practice

Apple had a WWDC 2012 session on optimizing web sites for high DPI displays. Interesting but not terribly complex stuff. I think if you follow the best practices they outline you can feel pretty confident your site will look good on a high DPI display. If you have a high enough resolution display you could always switch to high DPI for testing.