One major flaw with Google Analytics is its last click attribution which simply distorts your view of where traffic is coming from. If visitor first came via a Tweet, reads about your product and the next day he searches or types in your web address, GA would attribute the last traffic source as the real source of this visitor. You would never realize that it was tweet that brought him to the website.<p>Seldom any visitor converts on first visit and so it becomes extremely hard to calculate true conversion rate for different mediums in GA. How would you know which medium is most effective?