Because 1080 vertical lines equals a HDTV 1080p image size, and economies of scale mean that 1080 pixel tall display panels are less expensive than their cousins (because they double as televisions). And because they are less expensive, every monitor maker has decided that "1080p should be enough for everyone".

Our eyes are positioned next to each other on the horizontal plane. This is why a screen ratio with a larger width rather than height makes sense.

Except it's well-known that humans read more quickly if lines of text are kept short (around 6" or so). The height of a page doesn't significantly affect reading speed (ignoring scrolling). So it makes more sense, for reading, to have a narrow, tall monitor. (This is why LaTeX defaults to wide margins BTW, and I'm pretty sure this is why Kindles etc. are portrait-oriented.)

Even on a narrow monitor, all websites since suck.com use snake text these days, so the width of your text columns is likely to be unaffected. The only exception left seems to email software created by Unix folk who prefer all text to be forced to 80 characters wide monospace.

Using a narrow monitor will only lessen the amount you scroll.

Monitors are not only used for reading, for watching movies and playing games 16:9 is better than 4:3.

I don't need 1:1, but I'd love some large format 4:3 sizes.

I have a 30" 16:10 Apple Cinema display as my main monitor and a rotated 4:3 20" HP LCD on my right. While I like the 30" monitor, I'll admit the sides of the screen go to waste. But I love the height, and I like being able to compartmentalize onto the second monitor.

In my mind, a great setup would be two 4:3 equivalents of the 30" display side by side. So instead of 2560 x 1600, it would be 2133x1600. Same height, less width. And I like having two because of the organization issue.

Buy one and rotate it sideways (all modern OSs have support for this and plenty of monitors rotate freely).

The problem with rotating displays is that LCD pixels tend to be taller than wider ( http://en.wikipedia.org/wiki/File:Pixel_geometry_01_Pengo.jp... ), hence if you rotate a display it degrades the image quality. Cleartype especially starts looking horrible.

I remember what a breakthrough it was when Radius came out with a CRT that could be pivoted to display in portrait mode: http://www.youtube.com/watch?v=Dh5175Q4Vgo

We had one in the computer lab at my school, I would work late in the evening just to get some time on the Radius monitor.

You can still buy 4:3 monitors. I have a 27" center monitor with a 19" monitor on each side. I love it. Unfortunately, though, 1600x1200 monitors are pretty pricey for the size.

What 27" 4:3 do you have? I looked for large format 4:3's a while back with little success.

Sorry, my 27" is 16x9 and the 19" on the side are 4:3. Didn't make that clear in the post. Just saying it's a good way to go :)

I think it's because it's easier to move your head side to side than up and down.