The multithreaded performance optimizations are really interesting, however - but I'd be much more interested in this making it into mainline Node, rather than using this crazy closed-source fork. You're not going to find me using anything closed-source on my servers if I can help it, least of all something like Node which is hackable to its core.
If the performance improvements really mean something, and mean something outside of contrived for() and fib() loops, I hope the Node core teams have a serious talk with these guys about a merge. Node's cluster module is definitely not the final solution for properly utilizing a server's full capacity, and the team knows it; that module has been at level 1 (experimental) for a long time.