I've used Cell as a desktop CPU thanks to Linux on the PS3. It shows up under /proc/cpuinfo as dual core 3.2GHz. It's fine for general usage, but the lack of RAM and 3D accelleration slows it down a bit. I'd love to try it with more RAM and unrestricted access to the hardware.
Well at least it's not multicore (unlike many other "ng solutions" proposed by users) so in theory there wouldn't be wasted performance on "amiga-like" platforms.
Of course someone would need to write some API for programs to reserve one or several SPU's for use in some specific task (the easy part) and people would have to adapt programs to offload some processing to SPU's, when available (the hard part) and also have a "traditional" version to use in case, where no SPU's were free.
Let me put it this way, in a way it would make slightly less sense than f.ex. some quad core CPU