Translation/Explaination for non-geeks
The web is created by many different scripts and langauges that direct a browser to display content in a specific way. Many of those standards are set forth by the W3C committee, such as HTML. A browser must decide what to do when it reads the websites code. Put a picture here, align some text here, etc. If the browser fails to implement the standard correctly, a good coder's effort is useless. No matter how well the web developer writes code and verifies it against the set standard, it's going to be displayed as though they did a bad job. In reality, it's the browser who is to fault.
For those of you who wonder how come things seem to work fine in IE6/7/8 on major websites, despite results from the Acid tests, large well-funded websites have MANY web developers. Entire teams of people who specialize in these differences, and will design seperate websites for each browser. These seperate sites take in to account the problems, and are tested against the browser; not the standard. They then use code to determine what browser you have, and display the correct one for you. For a small hobby website with one or two developers, this process can take many hours of pulling your hair out and banging your head against the wall.
Because IE6/7/8 is disappointingly the majority of web users right now, they will make sure they provide a decent site for Internet Explorer customers. This is only because Windows is the common operating system and it ships with IE. People use what is easy, close, and familiar, and unknowingly TERRIBLE. Internet Explorer 6 is partialy to blame for the massive amount of spyware that ended up on people's computers. I encourage you to learn about browser basics, and choose a quality web browser. There are many factors that go in to this decision. Features for the user, security, performance, and ability to display the website correctly.
The acid test is an example of website code designed to display content that should appear correctly if the standard has been implemented perfectly. Thsoe who do not follow the standard will get an incorrect picture. There have been several versions of the acid test, and we're currently at version 3.
If you want to read all about it:
http://en.wikipedia.org/wiki/Acid3
Otherwise, skip to the good stuff. The screenshots from browsers:
http://en.wikipedia....hat_do_not_pass
IE7 is my favorite, not even close:

IE8

Firefox 3.6.4

This could easily turn in to an arguement about operating systems or prefered vendors of computers, such as Mac vs. PC Please, for the love of the internet, don't start that. Keep arguements/discussion to the browser level only.


















