At the moment I don't see any reason to create any business applications in Metro style.
Most companies will just lock out Metro and keep Windows classic desktop for their applications.
Metro apps "suspend" when they are no longer in focus.
This seems like a backward step especially when you are using a multitasking OS.
The rules are if the application takes more than 15 seconds to load, it is killed off.
When your application is notified it's going to by suspended you have 5 seconds to save any work. If you do not save the work in time, you lose the data.
So far these times are fixed and not configurable.