And now that I'm talking about UI design, here's another thing that's hard to do in DHTML and I hope it stays that way: Drag-and-drop. It's the least discoverable UI feature that I know of. All Windows IE users should try this: Drag the page icon in the topleft corner of this window onto the Home button. How many of you knew that that icon was dragable, and how many knew you could drag urls onto the Home button?
Jake: While I agree that the three user actions Sjoerd lists are easy enough for my grandma, I'd have to add that even my grandma understands pulldown menus. Anyone with rudimentary computing skill knows what to do with a pulldown menu when they see one, since nearly every Windows and Mac application has a menu bar.
Yes, everyone knows how a menu bar works, but not what it's effect is in a webpage. Read Drop-Down Menus: Use Sparingly by Jakob Nielsen. A menu bar is used for issuing commands, not for navigation. Even if the user understand that this menu is used as a navigation tool (most people have discovered that by now), it is a clumsy tool. You force the user to look through all menus to find the page they're interested in, if they find it at all because you had to label each page with an extremely short name. For webpages it's often better to give the user a limited amout of choices, and clearly describe each one of them.
The Standard: "Consortia like XML-RPC, which lets multiple operating systems communicate clearly, hint at promising ways that closed and open systems can interact." [Scripting News]
And another quote from that article that I like: "Less complaining, more coding. A company can't "embrace and extend" your product if it can't keep up with you.".