Here is the input extension to make a text field (actually, _any_ input, but you can add that logic yourself:) ) self clearing:

Requires Prototype Javascript Library!
I used v1.6 but I’m sure others will work fine.

// input_extensions.js

// extends HTMLInputElement to include a self-clearing method
// @author Rob Hurring
// @date 2008-04-23
// UPDATED: 12/02/08 -- thanks to Shawn for pointing out the IE flaw

var SelfClearingInput = Class.create();
SelfClearingInput.prototype = {
	initialize:function(element)
	{
		this.element = $(element);
		this.original_value = this.element.value
		Event.observe(this.element, 'focus', this.focus.bind(this));
		Event.observe(this.element, 'blur', this.blur.bind(this));
	},
	focus:function(e)
	{
		if(this.element.value == this.original_value)
			this.element.value = '';
	},
	blur:function(e)
	{
		if(this.element.value == '')
			this.element.value = this.original_value;
	}
};

when you want to use it, something like this can work:

// In your javascript file somewhere
document.observe("dom:loaded", function()
{
	new SelfClearingInput('ID_OF_INPUT_BOX');
});

Apocalypse 2.0 – the day the web broke by ZDNet’s Ryan Stewart — On February 16th, 2005, Jesse James Garrett coined the term Ajax in an article titled “Ajax: A New Approach to Web Applications”. Days before that, on February 8th, the Google Blog announced something called Google Maps. Ajax was born and the web hasn’t been the same since. The combination of JavaScript, DHTML and CSS seemed to breathe a new kind of life into the web. All of a sudden you could program a series of hacks and your web page didn’t behave like a web page before. All that time you spent learning JavaScript? With Ajax, you were in demand again! People started saying things like “JavaScript Engineer” with a straight face.

Heres the JavaScript includes

src="/jslib/prototype.js"

src="ubrious.js?domain=blog.ubrio.us"

or

src="ubrious.js?domain=<?=$_SERVER['SERVER_NAME']?>"

And the JavaScript itself

Event.observe(window, 'load', function()
{
	domain = '';
	$A(document.getElementsByTagName("script")).findAll( function(s)
	{
		domain = s.src.match(/ubrious.js(?.*)?$/);
		if(domain)
			domain = domain[1].replace(/?domain=/, '');
	});
	$A(document.getElementsByTagName('a')).each(function(l)
	{
		if(l.target=="_blank" || !l.href.match('/'+domain+'/') && !l.href.match(/^javascript/))
		{
			// attach if outside of your domain, and not a javascript link..
			Element.addClassName(l, 'aexternal');
			l.target="_blank";
		}
	});
});

Finally, the link classes

.aexternal{
	background: url(imgs/aout.gif) right no-repeat;
	padding-right: 12px;
	}