Does dbms_system.set_sql_trace_in_session work in 10.2.0.4 database?

 I have tried to trace a session in a 10G database using:

"exec sys.dbms_system.set_sql_trace_in_session(sid,serial#,true)" and it says the pl/sql executed successfully however it does not generate a dump file in my udump directory. 

Is this procedure still supported in 10G (I use it all of the time in another 8i environment) or is there a new/different procedure that I should be using?

I need to trace a session that is different from my current session and yes, I am issuing the corresponding "exec sys.dbms_system.set_sql_trace_in_session(sid,serial#,false)"  statement to turn off the tracing.  And I have verified that the parameter user_dump_dest is pointing to the correct directory.