I use Picasa as my ordinary photo tweaking tool. It's not Photoshop, but it does do stuff.
Now I only do photography for fun, so I've been fooling around with some of the transformations available in Picasa. This one is called "Orton-ish", after Michael Orton's slide overlay work. His stuff is more complicated than what Picasa does to mimic it, but it's still way cool. At it's simplest, it's stacking slides of the exact same shot, but of different sharpness to make a composite image. You can google Michael Orton if this technique interests you.
I'm old enough to have tried Ansel Adams "dodge and burn" techniques in the darkroom. He was a better photographer and printmaker than me, so it worked great for him, less so for me. I mention this because I have no problem with using whatever tool is available to change a photograph. We all shoot a bit wide and then recompose by cropping, although I know one photographer who consistently composes brilliantly at shoot-time. I'm not that good and never will be. But why not use anything to create the image you imagined when you shot it? The craft of making a photograph is the craft, but the pre-visualization of the image is the real work, the hard work. I know I'm not there yet, but I keep at it.
So here's how Orton-izing a couple of photos I like went.