Jagged white edges around partly transparent textures in GUI

We have an issue where we are using partly transparent textures for the GUI, and when they are displayed in the game(via OnGUI), they have jagged white edges.

Here's an example of what we're seeing: Jagged Edges

Anyone know why this is happening?

http://answers.unity3d.com/questions/2827/messy-alpha-problem-white-around-edges

http://www.youtube.com/watch?v=sMR_R72bWzw

Try turning off mipmapping, that usually helps, as otherwise the mipmapped version has a slightly larger area than the original, bleeding through to the white surroundings