I was going to post this as a reply to hfb's comments on my previous journal entry.
Since it changes completely the topic, I decided on posting it here, as a new entry.
Another problem with correct looking pages is that sometimes you want to have one appearance, that can be obtained in all browsers, but isn't 100% valid HTML.
It happens specially with layouts where you want certain things centered of with a different alignment.
To get the correct result, you either have to change the code or fill it with lots of other elements (such as anchors and divs).
Or, if you're using tables for your layout (instead of frames), you need to put certain things before using block elements inside one cell.
But, I believe that having a 100% validating page is worth this extra job. To be able to say that if you can't see the page you have a problem in your browser is very interesting.