I know plenty of users who hate typing on their mobile devices with small keyboards that tend to lend themselves to "fat fingering" keys, yet they still need to take notes on a regular basis. If those notes are for personal use and don't need to look professional or if you need to quickly draw up a diagram for later use Henry Huang's Whiteboard is a great option.
The Whiteboard application offers a very simple interface that couldn't possibly be any easier to use. I started by choosing the marker color I wanted to use, there are currently 4 colors: Black, Blue, Green and Red which can be clicked on from the left side of the program. I was then able to drag my finger across the screen to mark up my display with words, diagrams and doodles in the color I chose.
You'll also notice a "white" object at the bottom of the screen, this is the eraser which can be chosen to erase any part of the board you've drawn across. It's basically the same type of functionality found on MS Paint in a much more simplistic manner. Users can choose the on-screen eraser or use the volume down key to undo a marking and volume up redo a move.
There are also several other functions including screen sounds and "always on" screen functions which can be found by accessing the programs on-board preferences section.
Finally, users can choose to save their files as JPEG or PNG files as they see fit. I like the small size, yet crisp pictures provided by PNG files so I chose this option which then saved the files by choosing the "save" option from the menu screen shown above.