The Lens Baby is a very interesting device. Basically it is a very creative, highly maneuverable, low quality lens that turns your $5000 digital SLR into a $12 camera. So why would you pay money for such a thing? Because it will give you an enormous creative kick in the pants — even if you were to use it just once in your life.
One of the themes of this site is that often making a photo a little harder to see into makes it more interesting. Softening everything but a small area will always bring the viewer to that area. At the same time, the distorted area tends to bring a very strong aesthetic to the image — sometimes a wistful quality, other times a happy, giddy look.
Bottom Line: The Lens Baby produces a distorted image that is so compelling that it might make you rethink your approach to photography.
Why not just take the shot with a normal lens and then introduce the distortion in the computer, where you have the option of much more control over how you mess with the image?
I actually tried this right here: panel 6 is a Lens Baby shot, panel 7 is my fake-up of the Lens Baby look via Photoshop, and panel 8 is the original sharp image I used to create panel 7. So I claim that you CAN add a Lens Baby look to any photo.
So why the Lens Baby? Few of us commonly take a sharp photo and then distort it in computer to produce the Lens Baby look: it feels too manipulated, somehow. And putting the Lens Baby on the camera and taking distorted images feels much more genuine. I think this may change over time and I realize that some people DO distort their images in computer and that there is even software available just to do this.