Take Me To Your Leader.....by
espy2Comment: I think the DoF looks very unnatural here. If you are going to fake blur in post processing, you should study the basic principles.
The further something is away from the focal plane, the more it should be out of focus.
Therefore the person closest to the camera should be more blurred than the person between them and the person in focus.
Equally, the guy in green should be more out of focus than the people in blue cos he is further away from the girl in focus.
Since you have created so much blur in such a small physical area, the background, which is much further away in comparison, should be completely out of focus and extremely blurred, so detail is hardly seen. This is one of the main things that gives away your blur is fake. The background is just as blurred as the other people, no more.
Also, there seems to be very sloppy selection around the person in focus, since the trees in the background above her head are perfectly in focus! Also, some bits of her hat are out of focus despite being in the same focal plane as her.
If you use Photoshop CS for editing there is a "Lens Blur" effect which will blur different amounts based on an alpha mask you can create. Basically, in focus things are white, and everything else is darker, with black being the most out of focus. You can paint gradients and objects in different shades of grey depending on how far away from the focal plane they are. Then the tool does all the blurring for you, and also can apply lens aperture effects to highlights, which does give a very different appearance to "Gaussian Blur".
To sum up, blur is a gradual effect, not an "on and off" effect. You should try to experiment in photoshop to get the effect looking realistic before entering a shot here, or you will get a lot of people voting you down for bad editing.