Exactly. You shouldn't slap a ton of these buttons on your site and assume your maximizing your sharing potential. The 3 share links I have on imgfave.com drive 10x the traffic of the addthis widget that I used previously. I tried using the facebook like button, but the share link I have on their now drives 15x as much traffic as the like button, even though it takes two steps to post back to facebook. Important to make no assumptions and keep testing.