The Memory Warning icon has been included to help with users who have experienced crashes in the application. After testing and collaboration with beta users, it appears that most of the crashes that have been experienced since 1.0.3 are due to the iPad running out of memory and closing the application as a result.
The memory warning icon indicates that the OS has detected memory is low. That does not necessarily mean that the app is about to be shut down, rather it indicates that the OS is trying to clear up memory to let the app continue operating. If you see the memory warning appear on the toolbar, you can also quick save your painting if you are concerned about crashes.
Clear the memory warning icon and if it appears again shortly (especially directly after doing something that uses a lot of memory such as adding reference images or tracing images, or duplicating layers that have lots of paint in) we would suggest closing all parked applications and rebooting your iPad