I've used this technique as Les has described it (multiple exposures using different apertures). It's effective and interesting with the right subject, but every time I've done it the end print has been a little too "gimmicky" for me. I was basically looking for a way to emulate a soft-focus lens in some forest shots...I almost got there but never quite got what I wanted. It's a technique I'll probably re-visit at some date in the future with the hope of perfecting it, but for now I have about a dozen other things that are more important to me to work on.
Having said this, if you shoot roll film with a camera that will allow multiple exposures, give it a shot sometime. You'll only be wasting one frame, and you might find a technique you like in the process.