As Derrel says, depends. I've used it in family gathering situations very effectively, where a straight bounce off the ceiling leads to racoon eyes, but it IS inefficient in directing light, so it's effective range is quite short, and it doesn't work well in larger rooms.
I've made a DIY diffuser that is more directional, but the size of the lit surface is still relatively small (about a foot square), and the light is not as pleasing as I would have liked. I like the idea of Christina's diffuser, but don't have any experience with it (may have to get it to experiment with).