SB900's Diffusion Dome versus Gary Fong's Light Sphere

"They work well in small rooms with nearby walls, but they are not well-suited for open spaces. Just saying that so you know what they can and can't do. Plus, next time you see a wedding photographer using one outside (and they do that a lot) you can feel just a little bit superior." from http://strobist.blogspot.hk/2006/03/lighting-101-bare-tube-style-lighting.html