My apologies for the long silence...  I have taken all of the comments
received and integrated them in a new version of SRFI-18.  Many things
have changed so I suggest that interested parties re-read the whole
document.  You can find the new document at this URL

   http://www.iro.umontreal.ca/~feeley/srfi-18.html

I hope the SRFI editors can copy this document to the official SRFI-18
web page soon.

Main changes:

1) Weakening of fairness constraints
2) Clarification of the semantics of continuations and memory coherency
3) Addition of a "time" datatype and timeouts on synchronization primitives
4) Addition of an exception handling mechanism and multiprocessing exception
   datatypes
5) Removal of thread-startup!, thread-result, thread-end-mutex
6) Addition of thread-join!, thread-sleep!
7) Addition of thread-min-priority and thread-max-priority
8) Addition of condition-variable-wait!

Marc