We track user specific actions too but that is more for providing a personalized experience for the user (this is specific to our use case). We notify users of why we are collecting that data. To get an idea of what feature is popular we don't need to know WHO is using it rather HOW MANY are using it and for HOW long? Another reason to do anonymized tracking would be to address any privacy concerns users might have. If someone raises such a concern we have data we can show that says we did not do any user specific tracking.
This is specific to our use case and in other cases it might be important to track who is using what feature.