Preview's new "Magnifier"
Preview has an interesting new feature in Lion - the magnifier tool. Bringing it up allows you to take a closer look at a certain area of an image without having to zoom in the entire thing. There are two different ways to activate it: Either choose “Show Magnifier” from the Tools menu, or simply press the ` (backtick) key.
Once activated, the magnifier follows your cursor, allowing you to move to to different areas of the image. It seems to be yet another feature that is iOS-inspired — it feels very like the iPhone text selection “loupe”.
You can adjust the size of the magnifier using the pinch in and out gestures, allowing you to zoom in further and further until the magnifier occupies the whole screen.
Using the magnifier on PDF files brings up a slightly different, rectangular magnifier. Its size and position also subtly adjust to the content it is magnifying. For example, it will “lock” to the width of a paragraph, which is really useful when scrolling down a page.