The CITI event was a real disaster, likely enough for the importance of UI design to be taken more seriously around the world. IMHO, there are some quite good contributions in this thread with several excellent ones.

I will chip in my 2 cents from my experience on both sides of user interfaces:

In parts of user interface (UI) design, there has long been a principle that to make good use of the UI the user should have accumulated experience with the UI where they ran essentially experiments to discover how the UI and associated system worked.

So, with this principle, the CITI people just needed more experience with experiments, at ~$900 million per experiment!

So, right, the principle is flawed and for some applications expensive/dangerous.

While this principle of users getting experience from experiments has worked for the UIs of a range of applications, to be careful a principle should be that a user should be able to use an application as intended the first time and with no experiments.

Case 1. Last week I went to the Web site of my bank and used its UI to transfer some money from one account to another. The experience was Excedrin headache #394,325,757,110: I entered the data, and nothing happened.

So, I had to start running experiments. I hit Enter and left/right single/double clicked on everything in the window, and nothing happened. It appeared I was seeing all of the window horizontally, so I checked vertically, and to do that I looked for a vertical scroll bars. There were none. So, I converted the application to full screen and still saw no vertical scroll bars or way to make the money transfer happen. So, I did some more study and finally discovered that the window was so tall that the bottom of the screen was hidden by my tilted keyboard, and the part I could not see had the HTML push button for approving the transfer.

So, the UI designers just assumed, insisted, never told anyone, that, naturally, of course, all the users will be using their Web site with the windows expanded to full screen. And for some reason, whether their window is full screen or not, the UI designers don't like vertical scroll bars. The screen for the transfer had only a few lines of text and didn't need so much vertical screen space, but the designers seem to like using as much screen area as they can.

Okay, I learned how to use their UI. Still not so good: (a) The bank keeps changing their UI, and in this case made it worse. So, with that bank I will have to go through such mud wrestling nonsense several times a year. (b) To me, the original HTML controls were nicely designed, including the scroll bars, and one result was that nearly all the many millions of Web pages worked somewhat the same. Then somehow many UI designers wanted their screens to work in some unique way until they changed to another unique way a few months later. The power of JavaScript made this problem much worse.

Case 2. Also last week, in a weak moment, I decided to get a user id and password (PW) at one of the social media Web sites. They stated some rules for passwords; I followed those and typed in a password in a file where I keep such things; copied that PW to the system clipboard,
pasted it into their HTML single line text box for passwords, and nothing happened. I hit Enter, clicked around, etc. and nothing happened. I pasted the password in again, reloaded the page, closed the browser and tried again, etc. and nothing happened -- no messages, nothing. I still don't know what is wrong except it isn't me.

As I've mentioned at Hacker News before, for my startup I have 100,000 lines of typing of software for a Web site ready to go live. In that code I used eight design principles in UI: (i) No icons. Instead all the links are words in the English language that clearly describe the function of the link. For icons, I usually am not sure what they mean, can't look them up in a dictionary, and can't pronounce them, spell them, or type them -- IMHO, bummer. (ii) There are no acronyms. None. (iii) The only controls used are standard HTML. I wrote no JavaScript at all although Microsoft's ASP.NET wrote a little for me; apparently it has to do with cursor positioning but is optional. (iv) Each page (screen) has a link "Help" to explain the screen in detail. (v) Each screen has both vertical and horizontal scroll bars. (vi) The screens are designed for a window 700 pixels wide and are still usable in a screen 300 pixels wide. (vii) All the fonts are large and have high contrast. (viii) All HTML control bounding boxes are bold and black with high contrast. IMHO (i) - (viii) help UI design.