If you’re tired of explaining the same things over and over again, then you might find this little application for Mac OS X and Windows very helpful: Jing. It allows you to create screenshots and screencasts from any area of your screen and add annotations or voice-over to it.
Once done, you can upload your image or movie either to the default provider Screencast (free within some bandwidth and diskspace boundraries), send them to a FTP server of your choice or save it locally.
Jing uses a simple interface and an original, but maybe not overly practical “sun” hotspot for invocation. However, on Mac OS X a setting exists which replaces the “sun” hotspot with a normal menu bar item.