Adding noise to a gradient image background is something I do often in photoshop. It helps avoid color banding when printing. It can also be a nice little effect when used correctly.
While I’ve used InDesign’s ability to add noise to my drop shadows and glows using the Effects panel, I never consider the ease with which I could avoid doing it all in Photoshop… that is, until I came across this Tip of the Week from Mike Rankin over at InDesignSecrets.
Add Grain Effects to Photos and Type shows you how easy it is. And for those that do use the Add Noise feature in Photoshop, you know how much storage space this is going to save you!
There are lots of ways to sharpen an image in Photoshop, and there’s really no right or wrong way. But there are better ways than others. I think you’ll find the following method to be interesting, and provide pretty good results. 
First, place a copy of the image on a second layer by hitting Command + J. Set the newly duplicated layer’s blending mode to Overlay. Now go to the menubar and select Filter>Other>High Pass. Use a starting value around 4 to 6. You can adjust the values to your liking.
But I’m lazy, so I’ll go even further into the “easy” method. With Photoshop CS2, Adobe added a nifty little filter that does, among other things, vignettes. Here’s how it works: Make sure your image is in RGB mode. Select Filter>Distort>Lens Correction… There are several sections of this filter, but we’re going to use (obviously) the Vignette portion. First thing you may want to do is turn off the grid with the checkbox at the bottom of the dialog window. Slide the Amount slider under Vignette toward darken. This adds darkness around the edges and corners of your image. Now you adjust the amount of vignetting with the Midpoint slider. Move it to the right to have less of the image darkened or to the left to have more of the image darkened. That’s it. You can also apply the same technique to a layer filled with white above your image and set the layer effect to Multiply – this will allow you to adjust the darkness later if you wish.
After running a filter in Photoshop, you can reduce the amount of effect the filter produced by clicking Edit in the menu bar and select Fade…. This will bring up a dialog box which will allow you to customize the settings of the filter reduction.