Yup. Good design is everything. It's end to end.
The Windows Phone team has published an excellent resource outlining the design process that most designers including myself go through. This structured process is not tied to just mobile development. It can be applied across mediums. If you're new to designing apps, sticking to a rigid process is an excellent way to ensure you're thinking through all of it. Bless their kind hearts. They're also giving away templates you can apply to each stage.
I'm going to start things off with this. I'll be looking for this touch everywhere. Thanks for checking out release number two of my site.