You can set the CPU affinity for specific processes on any modern operating system. Maybe you wanted to set this for every process that the application will launch? It's still possible, but even less user-friendly.
Well... a nice dropdown in system preferences with something like "Allow any program to use no more than XX processor cores". Plus an editable list of exceptions at the bottom, where you can add serious things like Photoshop, SQL servers, compilers, etc.
I'll be seriously terrified by espn.com when Flash becomes multicore-aware.
It's already possible to do true multicore processing in Flash Player 10 using the Pixel Bender runtime. It's a bit cumbersome because you need to write your processing kernel in the data-parallel Pixel Bender language and call it from ActionScript using the ShaderJob object.
However it's definitely worth it for any parallelizable data-crunching tasks because you get both JIT compilation and multicore support. (Flash Player 10 compiles the processing kernel to native x86 code on the fly and splits the work across up to 8 native threads, IIRC.)
