In the ninth part of my series on architecting Windows Phone 7 applications, Shawn Wildermuth discusses threading on the phone.
Source: Shawn Wildermuth's Blog
In the big picture, the applications you build for the Windows Phone 7 needs to super responsive. But the hardware is a phone so you have concrete limitations to what can and should be done on the phone. In the big picture, its usually better to shoot for perceived performance than try to overpower the CPU and GPU. So a judicious use of threading is important.