According to Mr. Fitts, when using a mouse or other pointing device, the amount of time it takes to point to something is proportional to how far away that something is and how big it is. While it might seem obvious, this is often overlooked when a program is designed. The easiest places for a user to click are the four corners of the screen and the pixel directly under the cursor. The reason for this is because the mouse need not be moved for to click on the pixel under it and the user does not have to think much when moving the cursor to a corner because as soon as it reaches an edge, it can go no farther in that direction regardless of how much the mouse is moved. The Deskbar is in one corner of the screen for this reason.
When you design the graphical interface for your program, make controls easy to click on. Toolbars that have a text label as part of each button are inherently easier to click because the labels add to the size of the buttons. A number of existing image editing programs use the secondary mouse button for a pop-up menu to access common features because the mouse doesn't have to move in order to bring the menu up. Researchers have even experimented with circular menus -- called pie menus -- which capitalize on Fitts' Law in order to make a menu as fast as possible. Your program need not go to such measures, but do keep in mind that teeny controls slow users down.