I agree with everything Marco Arment wrote, especially this bit:
I’m not sure I’d want a Retina MacBook Pro yet. I suspect that adoption of Retina assets among Mac apps will be slower than we saw with Retina iOS devices, and more importantly, Retina graphics for websites will likely take significantly longer.
Since non-Retina graphics look worse on Retina screens than on older screens, Retina MacBook users would have significantly worse-looking web browsing for a while — probably years, not months. So I don’t think I’d rush out to get a Retina Mac, but I wouldn’t necessarily avoid a Retina screen when it comes time to upgrade for other reasons.
This is the most glaring problem I’ve noticed with the new iPad that isn’t as obvious on the iPhone: graphics look dismal on such a large, high-resolution display. I’m going through the slow process of upgrading the assets on the websites I control to high-quality versions, but these things take time. Even after I’m finished, I suspect I won’t have upgraded all of the graphics, but rather just the global images.
I think Arment is right: this is going to be a transition period measured in years.