The Blur Sharpen and Smudge tools are artworking tools that can give photos a different perspective. Also useful for graphical work they are well worth learning. Here's a short overview and a video showing how to use them.
The shortcut for the blur tool is R
The Blur Tool
The Blur Tool does what it says on the tin - it blurs out sections of your photo or artwork. For all of these tools you will need to select a brush that is appropriate for the job you are going to do. You can manage the strength of the blur with the strength option.
The Sharpen Tool
The Sharpen Tool tightens up pixels that you select. The tool can be a little crude so it is worth playing with the options. Again how much you sharpen can be controlled with the strength dropdown.
The Smudge Tool
The smudge tool takes a colour that you select and smudges it into wherever you draw. It can be useful if you want to blur out the edges of photos, for action shots for example. To do this sample the area you want to smudge and then use the brush to fade out the edges. As it smudges it blends the colours around it with the one you have selected.
Tools in action
Watch the video below to see the blur and smudge in action. The photo is by Taosmax and apparently he was hit in the face shortly after taking the photo! What we are looking to do here is to blur out the background, then smudge it to give it more action. The blur tool is a quick and dirty way of doing this.