I was really puzzled by the design decisions behind the new Metro user interface. Not the graphical design decisions, those are actually quite nice and inspiring, but the technical design decisions (or at least those in the current developer preview which dates back several month and are subject to change within a few days, when the first public preview of Windows 8 will become available). Some info at http://www.tested.com/news/windows-8-metro-app-multitasking-will-mimic-mobile-apps/3564/ and https://wiki.mozilla.org/Windows_8_Integration.

Why am i puzzled? In short, Metro apps run one at a time, generally full screen (the exception is 2 side by side), an app moved to the background gets suspended after 5 seconds and must save its state (and do it fast), given the OS might kill it in case it needs more memory (cannot they just warn the user and ask to close some apps as Android does? Too geeky?). The reason for these design decisions is to save CPU time and so increase battery life. A good idea for a phone? Maybe, but with dual core phones becoming the standard and with Android offering better multitasking, this seems a bit strange to me.

Via: http://blog.marcocantu.com/blog/puzzled_metro_windows8.html

Yep, and you also could only distribute Metro style applications via Microsoft store. Remind you of someone?