Yes, i just finished a comparison for my upcoming eBook on visual communication basics for 3D artists.

Global Ambient, Global Illumination and Global Radiosity are not a whole lot different. But there are important differences, if your trying for the best. Note that i exaggerated the Radiosity setting somewhat, to make it obvious.
Notice the difference in the yellow ball in the bookshelf and the top of the marble railing in the Radiosity render.




Hope that answers your question :o)