There are several modes that let you define where the blur and sharpness is positioned in your image. You can also use a paintbrush tool to draw sharpness onto an image that is pre-blurred.
To use the software, you manipulate control points. At first it seems very counter-intuitive, but with a little practice it starts to make sense. Of course, this software is not going to duplicate what an expensive lens can do, but I found it fun to manipulate some photos from my archives and 'miniaturize' parts of the photos.
One thing I noticed was that at times loading and saving JPEG images was very slow. I also wish there was some built-in help to get you started, but the developer does have some good tutorials and a helpful videos on his website.
If you are looking to do this on an iPhone check out our review here. You can also simulate this effect in Photoshop, and we have you covered there too.
The software sells for US$14.99 and requires OS X 10.5 or later. It's worth a spin if you are interested in doing these kinds of effects.
Here are some examples I created: