For a person working with images all day seeing the pixel size of images in Finder can be very useful.

To get this feature in Finder press Apple(Cmd)-J and switch on the Show Item Info option in the window preferences. You will instantly see a second row of information below your image files set in a nice small blue typeface. It's actually white for the files on the Desktop.

This option will also show the number of items in a folder or the size of a volume and available free space, but these are less exciting than the image size for me.