I wans't using any style or skin in my project in Unity3D 2.6 and i was happy with the default font for GUI now after upgrading to 3.0 the default font has changed, is there any way to restore the previous font or at least change it (without using any skin or style)?
The old default font in unity was Arial Rounded Bold. You can always get a copy of that font, and import it into unity, and use it for the GUISkin (either by making a custom skin, or from code, by setting GUI.skin.font).