I've downloaded a .blend file recently and all of the interface elements look very small. I remember that there were an easy trick to make everything bigger (or smaller) when I was using Blender 2.49 long time ago. My question is how to do it increase or decrease the size of the buttons within the panels using User Preferences and without using it?
Go to the panel you want to change then CTRL and push the MMB . If you move your mouse up, the keys get bigger if you move down the keys get smaller.
In order to restore the panel size to the default setting move the mouse cursor over the panel and press Home.
pressing Numpad + or Numpad - you can zoom in or out on any window (or control) in Blender.
To resize the panel drag it with the left mouse button.
As an alternative, if this is happening on a file you didn't create, you can preserve your own default layout, uncheck the LoadUI box when loading the file.