Measure pixels and differences between design and implimentation.
pixDIF - utility for showing you the difference Between your design and website/application

Ive created an AIR application to help developers and designers measure pixel distances on their screens. You tell if you need pixDIF if you answer yes to any of these questions:
Do you ever find that you need to measure the pixel distance/size of something when youre not in Photoshop? Or, put another way: do you wish you could take the guides in Photoshop with you to the computer desktop?
Do you ever want to know what a graphical asset will look like in the context of a website or application. For instance, do you wish you could take an image and MOVE it around over your website to see what it would like like in various places before you start writing the code to place it there?
Do you ever have a website or application design that you need to break up into pieces and build into a working site/app? And then as you write the code you need to see how close to The Design you are?
If you answered yes to any of these then Id suggest taking a quick gander at the video overview below. It doesnt do a lot but it is very handy for what it does.

Features:
alpha fading of the image
turn the image visibility off
Create horizontal or vertical guides
drag the guides around
use the guides to measure pixel distances very precisely
use the arrow keys to move the guides - if its selected/red
or use the arrow keys to move the image/window around on your desktop
hold down the shift key to move 10 Pixels at a time you can free download pixDIF 1.0.1 now.