In Nov. 2010, Microsoft and PreEmptive Solutions introduced Runtime Intelligence (RI) for Windows Phone for developers to instrument their apps and get deep insights into user engagement with the apps they create.
PreEmptive released a new version, that makes the tool much easier to use: no more "starter template" and obfuscation is smarter and easier to configure. And, if you're in the "good artists borrow, great artists steal" camp: there're two new sample apps (one for Silverlight and one for XNA) included for your stealing/learning pleasure.
A couple examples of the data you can get from RI appear below in the screen caps from the RI portal.
If you're already using the older version of RI (prior to Nov'29,2010), you'll need to download the new version as the old version expired on Dec'17,2010. You don't need to sign-up again.
If it's your first time with RI, sign up & download the software. And, watch this quick-start video.