Track Previously Logged In Users in Visitor log


I had used another stats tool called Wassup and it had a really nice feature where it would highlight traffic from known past commenters or users. There must be some cookies set by wordpress that allows a past commenter or a wordpress registered user to be identified. Can this be easily worked into the piwik tool? This is REAL important to me to see that past commenters are coming back and still viewing the site to track behavior and what types of posts they like. Thanks!