The goal of the blur method is to identify areas in your design with a high contrast. Spots where the eye will tend to move. This can be achieved by crossing your eyes but it's hard to be consistent and it's not good for you.
This post is meant to demonstrate a technique, not discuss the design of the example which is github.com in this instance.
So, let's just look at an example. I have cropped a section from the top of the landing page of github, with a message.
Let's start by looking at the crop through a 5px Gaussian blur:
In this image, it's clear that whatever the green horizontal banner, and the four yellow rectangles tries to show - it's very important.
This is definitely the areas of most contrast.
Then, here is the same crop with 2px Gaussian blur:
At this point we see much more detail, and the dashboard tools and the upper right 'News Feed' link shows up more clearly.
Finally, this is the crop with no blur:
In this case, the heavy use of contrast was intended, and good. Your eyes were meant to be drawn to the notification. If you do this to your designs and discover areas of high contrast which really is of little or no importance, I think you should consider making it a more integrated part of the design.