What does the mapping type do on a mapping node? What do the four buttons (texture, point, vector, and normal) at the top of the mapping node do?  It by default uses point and I have never changed it.  But in the answer to this question David mentioned changing it to texture (which makes intuitive sense).  But technically what do these buttons do?  I have always thought the mapping node is the same as using a vector > split XYZ and math nodes to manipulate the components, in fact I often do this instead of a mapping node if I want to plug some other nodes into the values.
The mapping node works by changing the coordinate system. This is why (when left on the default point setting) you have to put in a larger number to scale a image down. What is you are actually doing is scaling the texture coordinates up.

When set to Texture you are still changing the Coordinate system, not the texture. The only difference between Point and Texture is that for texture all the values are inverted.

Try it, when set to point a value of 2 is required to make the texture repeat 4 times.
When set to texture to get the same repeating 4 times the value must be .5.

I would highly recommend going through the cg cookie tutorial (archive) about the mapping node.