How to monitor rollback activity after killing long-running session

Found this brilliant script here: http://www.oracle-wiki.net/startsqlshowrollinfo

prompt This query will monitor rollbacks of transactions after killing a job or session. 
prompt If the used undo records/used undo blocks count is going down, then the transaction is rolling back. 
prompt If they are going up, then the transaction is still running.
SET PAUSE ON
SET PAUSE 'Press Return to Continue'
SET PAGESIZE 60
SET LINESIZE 300
 
COLUMN username FORMAT A20
COLUMN sid FORMAT 9999
COLUMN serial# FORMAT 99999
 
SELECT s.username,
       s.sid,
       s.serial#,
       t.used_ublk,
       t.used_urec,
       rs.segment_name,
       r.rssize,
       r.status
FROM   v$transaction t,
       v$session s,
       v$rollstat r,
       dba_rollback_segs rs
WHERE  s.saddr = t.ses_addr
AND    t.xidusn = r.usn
AND   rs.segment_id = t.xidusn
ORDER BY t.used_ublk DESC
/

In my environment, the output looked as follows:

This query will monitor rollbacks of transactions after killing a job or session.
If the used undo records/used undo blocks count is going down, then the transaction is rolling back.
If they are going up, then the transaction is still running.

USERNAME               SID SERIAL#  USED_UBLK  USED_UREC SEGMENT_NAME                       RSSIZE STATUS         
-------------------- ----- ------- ---------- ---------- ------------------------------ ---------- ---------------
MYUSERNAME_XX_XXX_  1194   10616     670875   14088690 _SYSSMU22_1415974968$          1189502976 ONLINE

The USED_UBLK was dropping, so the ongoing rollback could be confirmed to the users.