I have several instances of Oracle running on an HP9000 server. One
production instance and several testing/development instances. Also, I have 3
listeners, LISTENER, LISTENER1, and LISTENER2, on the HP box. LISTENER is
listening for all the instances including the production instance. The other
2 listeners are listening only for the production instance. What are the
ramifications to the users on the production instance if I stop and then
restart LISTENER but leave LISTENER1 and LISTENER2 up and running?

None. The listener is a broker only. There is no connection between clients and
the listener as soon as a dedicated server process has been started or the
dispatcher has been contacted. There is only a very small chance a client tries
to connect during the short period the listener is not operational. BTW the
reload command in lsnrctl should do this in one shot, just like startup open
force with the database.

Hth,
Sybrand Bakker, Oracle DBA