That's nice. Like Martin said, it makes no sense to fall back to LLVMpipe because if you do need to fall back, then your system most likely is too slow to support OpenGL in the first place, and thus most likely has a slow CPU. The only other scenario I can think of is if it's a server with some esoteric graphics card, but then it would probably not use an X server to begin with, not even talking about compositing.
And yeap, the performance of Unity over LLVMpipe on my GMA 600 device is abysmal. Moving any window makes the screen refresh at something like 5 FPS. That's just not good at all, compared to things like XFCE desktop, where there are no issues like that at all.