From Web designers: you need a Retina MacBook Pro – Marco.org:

Even though it’s a small market today (although don’t forget about the iPad 3), it’s inevitably going to increase substantially in the near future. Don’t you want to get ahead of that? Do you want your site to be ready the first time someone views it on a Retina screen, or are you OK with it looking like garbage for a few years until you happen to buy high-DPI hardware?