Microsoft just released an update to the iOS versions of its Word, Excel, and PowerPoint apps that lets you use your finger or a stylus to draw on your documents. This could come in handy in a number of ways, depending on how you use the programs on your iPhone or iPad.
According to TechCrunch:
There are options for a pen line, highlighter and eraser, as well a number of different colors. The tool is also somewhat pressure sensitive, allowing you to create bolder lines by pressing your fingers down harder on the screen. In Excel and PowerPoint, you can also draw on top of cells and slides, respectively.