And once again I start with a picture of a cat, this time it's Pod who is happy to illustrate the Orton effect (she's usually happy to do anything as long as it involves food or sitting on someone). I've been pretty obsessed with it since someone asked me if they detected it in one of my photos on Flickr. I had no idea what they were talking about so whatever effect I'd achieved with my photo was purely accidental. They pointed me in the direction of a website that explained that it was named for a photographer called Michael Orton who sandwiched one in-focus image (over exposed by 2 stops) to one out of focus image (over exposed by 1 stop) to achieve glowing, impressionistic images.
Pod before Orton...
I mainly use Paintshop Pro to process my images, and to achieve a simple version of the effect I duplicate the background layer and use a hard light blending mode on it, then I duplicate this layer and put a gaussian blur filter on it. What you can also do is erase some of the blurring to emphasise any details. There are quite a few tutorials on the web for different image processing software and it's worth playing around with different techniques on the image as the results can be amazing. There's a flickr group just for Orton type images, and it also has a good tutorial.