So with Windows Phone 8 being announced and Windows 8 also about to come out. They look very similar, and also act similar. The design is the Metro design, and it is different then the other options out there today.
First a little understand about why the metro design is cool, it is designed to be “glanceable,” what this means is they want you to take a look at it and see important information at a glance. When you look at your phone and see see a number next to your email you know you have that many emails. When you check the lock screen of your phone and see a symbol with a number you know you have a message waiting. And to get that nice glanceable design they developed the metro design to make it feel universal. Just image you were in a foreign airport, and not knowing the native language how would you get around? You would look at the symbols and understand what they mean. This is what the metro style was inspired from.
So now why it is important to understand metro design. The whole windows 8 and windows phone experience is built on metro so you should design your apps with that in mind. They make it easy for you to design your app with metro with the blend software that comes with the windows phone SDK. and even give design guides. So when you are building an app for windows phone or windows 8 keep try to make it glanceable, have important information get displayed in the icon. make it smooth and easy to transition.
Check out this blog post by the awesome Jeff Wilcox http://www.jeff.wilcox.name/2011/03/metro-design-guide-v1/ it goes over the metro design basics nicely I think.
Remember Metro is the future, learn to design with metro.