Positives: I love this app! I use it frequently on my iPhone. For example, I'm at a game and I see someone I know but I can't remember their name. I take a quick photo of the person that is seated in a group. I use Skitch to draw an arrow to the person and send it to my husband to identify the person. Problem Solved! There are tons of uses for this app. For education, the possibilities are endless. It's user friendly so even the youngest (PreK), would be able to use it. One example is taking photos around the school of shapes and using Skitch to point the arrow on the photo to the correct shape, or taking photos of words that begin with a certain letter and then typing the word over the photo. Share a diagram and let students label parts using Skitch.
Negatives: To mark a PDF, there is a nominal one-time $1.99 upgrade charge. If you use PDFs frequently, it would probably be well worth the fee.
Below is an example using Skitch to mark a photo:
I give Skitch a Thumbs Up!