CSS

You want your pages to be W3C valid? Well! But if you own a website that has more than 10 pages, that may become a huge task to validate them all, one by one.

It's very annoying to switch your screen resolutions to test if your website is displayed correctly with other screen resolutions (800x600, 1024x768).

It is well known that Internet Explorer, especially IE6, gives incredible headaches.