The Mac OSX Snow Leopard Preview application does more than just open image files. It is also a much more flexible way to look at PDFs than using Adobe Reader.
This short video shows a couple of tricks that are easy to do to manipulate a PDF, or create a new PDF document from 2 or more existing ones. You may want to view it at 720p by clicking the up arrow beside the default 360 (that will appear when you play), and in full screen by clicking on the four arrows at the bottom right of the video window.
Preview can also be used to adjust images to a precise size, overlay text on an image, rotate it and so on. Experiment! And the best thing is that Preview is already installed in your Applications folder!
By the way you will note my desktop photos changing in the background. The photos are West Hill House (of course!) and places we have visited during our stay in France.