“Don’t buy this computer.” →
From Patrick Gibson’s review of the 13” Retina MacBook Pro:
While the Retina screen contains something on the order of a trillion pixels (or so it feels like), the effective screen size is actually smaller than the 13” MacBook Air. The effective size of the 13” MacBook Air is 1440 × 900, whereas the Retina MacBook Pro is 1280 × 800. If that doesn’t sound like a lot, it isn’t, but it does make a difference.
This shouldn’t be much of a problem for most 13” Retina buyers since the 13” MacBook Pro has only ever had a (pathetic) 1280 × 800 screen (and has sold extremely well despite it), but it will definitely be noticeable for people like Patrick who are accustomed to the 13” MacBook Air’s higher-resolution screen.
The 15” Retina has a similar effective-space downgrade: its native resolution is 1440 × 900 points, while the non-Retina 15” has had a 1680 × 1050 option for years.
As Patrick says, the 13” Retina, like the 15” Retina, can scale to a simulated 1680 × 1050, but it doesn’t look nearly as good. I’ve also found that when the 15” is running one of these scaled modes, it has noticeably worse scrolling performance.
In practice, I switch my 15” Retina between native and simulated-1680 depending on what I’m doing: native for writing and internet timewasting, and simulated-1680 for programming. (The 15” also offers a simulated 1920 × 1200 option, but everything’s too small for my comfort.)