A little tip for removing items from the dock which is usually located at the bottom of your Mac screen.  In the past, you simply had to drag the icon out of the dock and let go of the mouse button, upon which you would hear a little 'puff' sound and the icon would disappear.

In Mac OS X 10.7 (Lion) and 10.8 (Mountain Lion), this still works but it's slightly different and I must admit it caught me out a little at the start.  I was dragging the icon out of the dock and releasing the mouse button, but the icon would not disappear, it would simply jump back into the dock.

It turns out that you now have to move the icon a bit further away from the dock first and then wait a second before the little 'puff of smoke' icon appears.  As soon as it appears, you can release the mouse button and the icon will disappear.  If you don't do this, the icon will jump back into the dock.

At first I thought this was some kind of glitch or bug, but having looked more closely I know realise that this is intended to avoid accidentally removing icons from the dock, which actually was quite easy to do before.  The problem was, it wasn't quite so easy to know which icon you had accidentally removed!