One of the advantages of Apple's multi-touch gestures is that many times we already use them almost unconsciously with good results, but it is logical that sometimes we do not even realize that it can be used.
On the screen to choose the desktop background we can enlarge the thumbnails in a simple way by zooming with both fingers out which gives us at most to expand to a 2 × 2 table, while by default one of 5 × 4 is seen.
You can perform the gesture with any Apple accessory that is multi-touch, yes, in Lion.
Source | OS X Daily