When you're creating a presentation using Keynote, it's fairly common to add notes for you to use while giving your presentation (the information that you need to see, but don't want your audience to see). This is done by adding the text to the "Notes" area. This may not be the most ideal way to add comments while building your presentation, however. Rather than adding notes, let's add comments.

Below is a sample comment added to a sales projections page of a presentation for a Board meeting:

You can see that the look is very reminiscent of a sticky note. This is done on purpose. It's designed to bring attention to it. To add a new comment, simply click on the "Comment" button at the top of the Keynote window (if you decided to turn off the "Comment" button, go to Insert | Comment). The image below shows the same comment in the context of a real-world slide:

One thing to note about comments is that they are only viewable while designing your presentation. If you leave a note on a slide, and start the presentation, rest assured it will not be displayed.