Some very valid points, but those which say that having valid code makes your page perfectly viewable in all browsers is wrong. As far as i see things, it works in two ways

1) You use completely valid code, but your site may not work in all browsers as intended. Now you must address this probem by finding the problem, learning about how browsers render certain things, and applying more/different code to sort the problem out.

2) Leave code invalid, but use code which you find works in all browsers.

I've spent ages working on my Portfolio, got a basic design made in Photoshop, extracted external and internal background, default images, and a banner. Next was coding it, which is where it has gone all pear shaped. Check it out http://www.michaelbull.net/home.php (Temporary page for now, no links work, and still parts of the design are missing). In Firefox, everything appears perfectly, but when i open it up in IE, the box appears more to the left, even though most people pointed that validation would make your pages appear the same in all browsers. Now i've gotta find a way of fixing all this.