Yup, I'm with Balz... In the evening I need something warmer so I bring a down puffy. If its raining I need something that will keep me dryer so I bring either a rain coat or poncho. When I am hiking I generate enough heat to stay warm. There are some situations where a windbreaker would be nice but not enough to bring an extra piece of gear.

...they do seem popular though. To those who bring them, do you not bring rain gear or a puffy/warmer jacket?