Apple's iPhone Software 4.0, multitasking demoed in videos [u]
In order to deliver multitasking without incurring a performance hit in battery life, the iPhone maker said it has created seven different multitasking services for developers, each tuned to solve different multitasking scenarios.
Among them are Background Audio, Voice over IP, Background location, Push notifications, Local notifications, Task completion, and Fast app switching.
When combined with Apple's Dashboard-like user-facing interface for fast app switching, the end result is what can be seen from the below video of an iPhone 3GS running the first external beta of iPhone Software 4.0:
A more extensive walk-through of the iPhone Software 4.0: