This morning I came across this tutorial in Layersmagazine. It covers the use of clipping masks and brushes in Illustrator and Photoshop. Very useful if you're trying to create an organic grungy frame for your artwork.

"There has been a surge of "grunge" effects lately that have been created using Adobe Photoshop and Adobe Illustrator. So here's one more effect for your arsenal of grunge effects. In this tutorial, we'll show you how to create a custom brush and use it to create a really cool border mask in Illustrator, allowing you to apply it to a photo or graphic without affecting the original image. You can then take this mask and use it with any graphic that you want. It's simply a matter of getting used to working in mask mode." Full tutorial