More seriously, a big problem I see with a multiprocessor runtime (aside from implementing it) is that there are two radically different ways to go about it (map Scheme threads to OS threads, or extend the current lightweight threads so that the Gambit thread scheduler can take advantage of multiple processors). Several people think option 1 is the best because you get simple interoperability with C. But I think the second option is more interesting because it is more lightweight and it allows a very high number of threads (in other words I think the C thread model sucks). So I'm bound to displease a bunch of people whatever I do!
I'm not an expert programmer, but I would like to "cast my vote" in favour of the second option. Scheme is Scheme, interoperability with C should remain a lower priority. And not everyone needs the C interface...
P.S is that Opteron for real?