My only hesitation about using 'Proc' as the namespace is the association with the /proc filesystem on linux (and others).

What does everyone think? Does 'Proc' mean 'process' or '/proc'?

And reqarding system_as_user, fork_as_user, open_pipe_as_user, open2_as_user and open3_as_user etc... That is where this is eventually heading. The module containing fork_as_user and co would use Proc::SetUser or whatever the name turns out to be.