If you are looking for a way to quickly research the Windows Phone 7 applications in the marketplace, here is a nice tip. The latest version of Zune software for the desktop has a screen showing the Windows Phone 7 marketplace applications. All you need to do is open that screen and using Fiddler2, you can see all the web requests being made. A lot of them are web analytics posts. You will be able to see some that actually return an ATOM feed of data about applications! Which is awesome!
So, if you want to find out something like, say, all phone apps in the marketplace sorted by customer ranking, you can simply open this link in your browser. For additional sorting options, open up the raw xml and try using different xml elements in the orderby query string parameter.