What is this from, is it a Simply Maya video?

Looking at the mesh in question, I'd firstly say its got too many polys, compared to the other object. Have you deleted history and or did you grab any other faces by accident when you extruded?

Also do you know about the world/local icon for the tool when you extrude? it may be a case of positioning of the tool after you have hit extrude. Its usually something simple, we all do it, at every level.

Jay