While stressing that it's a personal suggestion, Andy Pennell has written up the use of Flurry's Analytics service and how to integrate the free service into your won Windows Phone applications.

Flurry is an analytics engine that you add to your app and then it reports as much or as little as you would like it to about your app, within about four hours. It is very easy to use (its documentation consists of a tiny text file), it works very well, and its web site lets you grok the information in an easy to use way. Oh and it is totally free!

Getting as much information as possible from users is always important to developers, especially solo devs and small houses, so using Flurry is a very smart idea - just remember to tell the users you are doing it and provide an opt-in or opt-out in your application!

All the tech details, code snippets, and report reading skills are on Pennell's blog post.