Should you be new to Windows Phone Metro UI development, coming from either Android or iOS for example, then this well worth checking out. Teppo Kotirinta, Principal Designer at Nordkapp, has just published an article on their blog announcing their designer cheat sheet.
This image which can be printed off or downloaded and opened on a 50" TV and will guide you through each illustration detailing what each screen contains and how the structure and design should be developed for effective deployment. Included are dimensions for live tiles, hex codes for all the WP7 themes and more. It really is a 101 for designing perfect Metro apps without the 1,000 pages worth of reading required.
They state that the cheat sheet will be updated as of when Microsoft release more features/information, so keep an eye out for updates should you find this useful.