I recently started trying this technique for portraits and below are 2 images that I tried so far.
First one is of my Twin niece which was taken in my home town.
Go here to view few more photos of the twins.
The second one is of my wife taken at K.Gudi jungle lodges.
I am not explaining this technique in detail here as there is already a good article by Richard Bui here
You can also visit Ryan's blog here
In the blog above, example images were taken using 85 mm f/1.4 lens which gives a very shallow depth of field. Since I don't have such expensive lens, I instead tried using Nikon 50mm f/1.8 lens and results were satisfying enough.