I've been a Bloglines user for a long time (January 2004), but recently I've started to play around more seriously with Google Reader. One of the really nice things with Google Reader is the myware aspect of the service, which lets you learn about your reading behavior.
For creators of web services myware is interesting, as it can be used to shape user behavior. Depending on what you track (and possibly reward), you'll make certain feedback loops stronger. As a result usage will change, possibly leading to an increased number of visits and more time spent per visit.
Feedback loops don't have to be myware that reveals each individual action to the users. In many cases revealing everything will lead to a subset of the users doing a task mechanically to gain status (if the feedback loop includes public recognition once a certain level is reached), rather than enjoying the service. And that is something you want to avoid long-term.
If the reward is private, i.e. how am I using this service?, my gut feeling is that you should give information on a more detailed level than if the reward is social, i.e. look I've been doing cool stuff on this service.