Investors who hold shares of Enterprise Products Partners (EPD -1.32%) probably feel pretty good lately. The stock has performed well over the years, and management has proven that it has its eye on the ball, and shareholders interests at heart. That doesn't mean it's time to stop paying attention, though. In this video, Fool.com contributor Aimee Duffy points out three things investors should keep an eye on at Enterprise, in good times -- like now -- and in bad.