Stammer. If a product or service takes 0.1 to 1 second to respond, users will notice a delay.
Interruption. After a second of no response, users will feel that the task they were doing was interrupted and their focus will shift from the task at hand to the product or service itself.User will also feel utterly frustrated, angry, and abandoned. And their hatred for the product or service will only continue growing. Also, user will definately continue not at all understanding why clicking a link opens a new WINDOW and not a new tab. Finally, user will be very upset and curse the existence of Microsoft, even though Win7 and Office mostly rocks.