A lot of times I find myself opening up Photoshop just so I can paste a screen shot of an application I'm working on in there and move some elements around to see where they look best. I might grab a button and nudge it over to one side until it lines up somewhere. And I use that info to go update my app.
Photoshop is way overkill.
To use it, take a screenshot. I use Skitch on OSX and just hit Print Screen on my Windows machine. Then drop or paste that screenshot onto Nudger. It'll load up the image. From there you can click & drag to define an area to nudge. Then move it around with the handles that appear. You'll get feedback while you do it.
Here's some screenshots (I'm working with a screenshot of the Flash CS4 splash screen here)
Step 1, right after pasting it.
Next, I select an area of the image with the mouse.
And finally I move it around.
The grid below the selection tells me the original location/size of the selection, the new location/size, and how much that differs from the original. If this were an app I was working on, I'd know I need to bump those objects over by 221 pixels and down 5.
Of course you can make multiple selections and move lots of stuff around.