Hello Damien,
   Back in 2005, I ask to the list why no one was talking about
implementing native threads in Squeak, I ranted a little, and got
seriously beaten up by some heavy weights of the community.
   The important thing is that, in spite of the passionate discussion
around the subject, VERY illustrative stuff about Squeak threading
model came up in that thread.
   So if you care to read a little about the problems of native
threads and green thread on Squeak and on different platforms as well,
my original post is here:

   http://lists.squeakfoundation.org/pipermail/squeak-dev/2005-April/090791.html

   You can probably follow the thread from there.
   Cheers.

   r.