With Preview in Lion, you can record your signature in Preview and then apply it to PDF files and other documents. Use your Mac's camera to take a picture of your signature. Add a variety of signatures and other stamps to your Preview preferences and use them with the annotations feature.
Learn how to use Snow Leopard's Preview application to cut out backgrounds or objects in images and photos. Preview has a standard Lasso Selection tool, a Smart Lasso tool and an Instant Alpha tool that can be used for this purpose. You can use these semi-transparent images on top of other images, in documents or in iMovie.
You can use Preview in Snow Leopard to merge documents and pages within documents. It works a little differently than it did in Leopard because you can have multiple documents in the sidebar which can confuse things.
You can go even further with Print As PDF by printing into Preview and then saving the preview document. You can reduce the file size or apply any number of Quartz filters. You can even make your own filter. You can also save as an encrypted PDF.
Preview was updated for Snow Leopard to include some powerful annotation features. You can now mark up documents and images with lines, notes, highlights and links.