It works _very_ well. We've developed a huge monster of an app here at
AT&T Wireless that runs on NT and mach. Other than a few niggling bugs (
which we've worked around ) and missing features on NT ( you don't get a
wait cursor for free on NT, you have to ask for it explicitly ), there are
no code differences at all between the mach and NT versions. It works so
well, that we've done almost all of our development on mach, and only
debug/test on NT when necessary.
If the MacOS YellowBox gets developed as planned, OpenStep will be one of
the best cross platform development environments. It wouldn't be a bad
idea at all for M$ to do ALL of their app development in OpenStep -- I
just don't expect it to happen in my lifetime....