For those unfamiliar with the term, this is actually referring to how do you write up the language behind the layout and how much do you write it according to the standard set up by The World Wide Web Consortium (W3C). To check whether any web is valid or not, go here. There is another part of the validation service which involve CSS and for the moment, the CSS script written by Blogger caused my failure as you can see below.
Is it important to get the validation? Personally, I don't think it is not that important to get the validation but by doing this, at least you know what mistakes occur while coding the layout. The best reason not to get the validation is many major websites do not follow the standard by W3C. Even google, yahoo and microsoft failed the validation :). The second reason would be that the main internet browser, Internet Explorer, does not follow the web standard too as you can see below. This is tested against Acid 2 Test.
Compare this with Firefox 2.0
If the browser followed the web standard rigorously such as Opera 9, the picture should look something like this
p/s: Right now, I am waiting for the match between Fernando Gonzalez and Rafael Nadal. This match will be quite interesting to see :)