Always - I Love 3rd party content, from new campaign settings, to new rules, I love it all and use what I want/am allowed.
Often - I use some material I find on the web, or in other publisher's books, but I am careful about non-official sources.
Sometimes - I don't like to use 3rd party stuff unless it really fits a need, and only then only occasionally.
Rarely - I tend to stay away from non official stuff for a few reasons, but on a very rare basis I will use it.
Never - I just stay away from non-official sources. Makes the game more balanced, easier, and better for me/my group.