How I Use It
I've visited classes where students photograph and mark up geometry in real life (e.g. measuring the radius of a clock in the hallway) using Skitch with iPads. I also drag Skitch screenshots into PowerPoint slides whenever I create how-to guides for students. If you're using Skitch to create guides for students, I recommend doing a Google search for "Skitch keyboard shortcuts."
Skitch makes it easy to take screenshots, mark them up with arrows, shapes, text, etc., and save them. It works on IOS and on the computer. On the computer version, it works especially well if you have a large screen, because then you can save your work very easily by dragging it into files, into Google Drive, or into Evernote. (See the "drag me" bar at the bottom of your Skitch Window.) The one annoying thing is that the computer version asks you very, very frequently if you want to update Skitch. Updating requires a few clicks and takes more than one minute. I’m pretty sure updating takes as long as installing from scratch.