I was just toying around with multithreading small parts of jiglibx today, small world… :)
I just wanted to say that if you're seriously multithreading JigLibX, make sure to avoid ThreadPool (and write your own thread manager that reuses threads)… The garbage generated from my own attempt at multithreading counteracted the benefits w/ jumpy GC's (on the 360). I don't know how many of the devs here develop on the 360, but it's also important that you have an option to select the Number+Affinity of threads so that we can make use of specific cores we aren't utilizing.
Anywho, good luck multithreading JigLibX, I can't wait to really test it out!
BTW, I'm running Windows virtualized on my Mac and only allowing it 1 virtual processor… so probably useless data, but both multithreaded and normal versions run around 7-8fps…