The majority of the articles/tutorials/blog post I read about Microsoft's Prism Framework center around Silverlight. With the composite model being an interesting model for an existing desktop app that needs a little TLC, I'm wondering is Prism a viable technology for a desktop LOB app?
It is for Silverlight(Web), WPF(Desktop) and Windows Phone 7(Phone).
Basically, it is for any platform that uses XAML, MVVM combo.
And for your last question, YES, it's a very good option to go with when developing a LOB application in WPF.
But remember, you will need to spend a few days just to learn Prism (and Unity or MEF). So, be ready for it.