I started using Jing over the summer, and have found countless uses for it personally and professionally.
Jing can be used to create a screencast or a screenshot. Screenshots can be drawn on and annotated to highlight information, or give more detail. My number one use of Jing has been giving teachers a visual guide to something that would normally be a long list of steps. Below is an example of a mid-year review that I needed my teachers to sign off on. Rather than create word based instructions, I sent this Jing.
Teachers found it to be very useful, and it exposed them to a new tool they could be using in their classrooms.
Jing also allows users to create screencasts. I use screencasts all the time to walk users through more complicated computer processes (see screencast below in my post on using Google Forms for walk-through observations). The free version of Jing allows for up to five minutes of recording. This seems like a lot, but five minutes goes quickly.
I hope you find Jing as useful as I have.