>How is Emacs' interface terrible? Is it the default key bindings? Is it the lack of mouse-friendly buttons and menus?

Off the top of my head, though my depth of knowledge of Emacs is almost more shallow than that of vim:

1. Discoverability. I had to reverse engineer Emacs' basic key commands, due to a complete lack of documentation on the first system I encountered an Emacs clone on; I was able to do it, but I have a considerably higher IQ than 120, thank you.

2. Key combinations are somewhat random. Some have mnemonics; most don't. Saying "change the keybindings, then!" is beyond the point; I'm talking about the editor UI as a new user would learn it, and by definition a new user doesn't know what keys things "should" be assigned to.

3. LISP, the write-only language. There's a reason the 1950s-designed language hasn't ever caught on. PG forgive me. Languages like Lua grant you 95% of the power of LISP, but are much more readable. And the last 5% is part of the cause of the readability problems of LISP.

4. Sometimes a mouse IS the right answer for some tasks. In an editor, this is MOSTLY not true, but when it is true, it's powerful.

5. Modern standard keybindings DO EXIST, and neither are supported by vim or Emacs out of the box. Ctrl-ZXCV, for example, will be expected by 99% of users to do the standard things. (If someone reading this is so Unix-centric they don't know: Undo/Cut/Copy/Paste.) Shift-arrows for selecting text. Shift-Control-Arrows for selecting word-at-a-time. Etc. Both Emacs and vim are (nominally) terminal-based, and you can't GET those key combos over a terminal.

6. Two-key combos that AREN'T shift keys for important commands (M-w). 'nuff said.

>Also, when we talk about "measurably, objectively terrible" interfaces, were the measurements made by researchers whose test subjects all had 120+ IQs? Those would be the only measurements that interest me.

I already commented on my own IQ, and I find it to be an irrelevant comment. A better UI tends to be better for any IQ. Do you really want to be using your IQ to decode your UI, or would you rather not have to think about it and instead think about the problem at hand?

I'm not talking about a dumbed-down, feature-poor UI. There are very few features anyone can point to in vim or Emacs that I haven't seen, typically way more easily accessible, in modern editors with decent UIs (I don't know of any with a really good UI, but most are better than their ancient ancestors, though I haven't done a complete survey recently, and so I should again).

And remember, I already said this is mostly irrelevant if you already have learned vim or Emacs. You've put in the time, and suffered the pain of their steep learning curves. You're past the hard parts. Enjoy your editors; I'm not trying to get you to change what you use.

To be honest, I'm not really interested in debating particulars. I'm sure you'll find SOMETHING to pick at in the list above; I know you CAN use cua-mode to get some basic standard control keys. But when a new user starts with Emacs, will they know to enable cua-mode?

The killer for me is that LISP just makes my eyes bleed. I've used it (in college) to create research apps, but I never liked it.