using multiple processors for ports builds and/or portupgrade(1)?

[George Hartzell]

I have a dual processor machine sitting at a load of 1 during a
"portupgrade -f gnome2".

Are the Makefiles in the ports trees safe to use with -j 4 or -j 6 on
a dual processor machine?  I'm worried about how the dependencies are
handled, etc....

If the make is a safe thing to do, is there a standard way to
encourage portupgrade to take advantage of it?

g.