On the BC page (http://minnow.cc.gatech.edu/squeak/BlockClosureVersion)
you will find a new BC version.  Its image format is slightly different
from the last version, so you need a new VM and image.  But this new VM
interprets bytecodes 20% faster and message sends 50% faster than the
standard VM according to 0 tinyBenchmarks on my i586 533MHz Linux
machine (the old BC version was only 10% and 33% faster).  Also, I fixed
a few notable bugs:  one was a conversion bug that I think may have been
the cause of the Mac problem;  another was the cannot return problem, it
now raises the error as expected; and the last was the problem viewing
block closure source code in the debugger (although I still haven't
fixed viewing do-its, which has no source).

Of course, I encourage interested parties on other platforms to build
VMs and post them on the BC page.  I would also be interested in
combining other VM enhancements (hey Scott) and posting them in a
different section on the page.

Cheers,
Anthony