Mouse Interaction

Remember that not everybody can use a mouse with equal dexterity, and that some users may have difficulty seeing or following the mouse pointer.

Don't depend on input from mouse button 2 or button 3. As well as being physically more difficult to click, some pointing devices and many assistive technology devices only support button 1. Some assistive technologies may not emulate the mouse at all, but generate keyboard events instead.
Allow all mouse operations to be cancelled. Pressing the Esc key should cancel any mouse operation in progress, such as dragging and dropping a file in a file manager, or drawing a shape in a drawing program.
Provide visual feedback throughout a drag and drop operation. As the mouse passes over valid targets, highlight them and change the mouse pointer. Use the "no drop" mouse pointer when passing over invalid drop targets. See Mouse Interaction Examples.
Don't warp the mouse pointer, or restrict mouse movement to part of the screen. This can interfere with assistive technologies, and is usually confusing even for users who don't rely on ATs.
Don't make mouse targets too small. In general, mouse targets should be at least the size of the "hot area" around the resizable window border in the current window manager/theme - bearing in mind that a user with impaired dexterity or vision may be using a window manager with larger areas than the default.