You need to make sure that your users see what you want them to see.

Rich internet applications can be fast, sometimes too fast. Because RIAs allow transitions to take place more quickly, users may not know an action has occurred.

For example, Gap.com provides an animation that indicates items have been added to the cart while on a browsing or product detail page. It is the fact that the animation slides down and catches the user's eye that confirms items have added to the cart.

Here is one example of a user-friendly animation window: