As someone who creates a lot of diagrams, I disagree. Most diagramming tools require me to spend 80% of my effort on layout issues to make diagrams look good. I would much rather have a mini language in which I can express my diagram than fumble around with pixels.

Doing things in text also keeps the diagrams Wiki friendly, which might be a consideration (it sure is for me), allows easy auto-generation, and so on.

I've been looking for a good tool in this area. Groff has PIC, which was created by Kernighan and sort of does this (this is what W. Richard Stevens used in his books, for example), but I want pretty colors and gradients and rainbows. I'd love to hear suggestions for tools in this area.

I am thinking about writing my own tool, maybe in JavaScript to use a familiar syntax and allow a sort of eval loop on the browser.

The idea is that you can do things like this:

    <img src="http://yuml.me/diagram/class/[User|+Forename+;Surname;+HashedPassword;-Salt|+Login();+Logout()]"/>

There is some advantage to having a text-based markup language. That way you can emit it from tools.