# SELECT * FROM pg_stat_activity WHERE usename = 'postgres' AND current_query ILIKE '%vacuum%';
  datid  |  datname   | procpid | usesysid | usename  |                                         current_query                                         | waiting |          xact_start           |          query_start          |         backend_start         |  client_addr  | client_port 
---------+------------+---------+----------+----------+-----------------------------------------------------------------------------------------------+---------+-------------------------------+-------------------------------+-------------------------------+---------------+-------------
 7651893 | master_dev |   20288 |       10 | postgres | VACUUM ANALYZE myschema.mytable;                                                  | f       | 2010-04-14 16:24:51.421088+00 | 2010-04-14 16:24:51.421088+00 | 2010-04-14 16:24:46.875911+00 | 192.168.24.63 |       54065
[snip SELECT * FROM pg_stat_activity]
   16389 | master     |    9596 |       10 | postgres | autovacuum: VACUUM ANALYZE pg_catalog.pg_attrdef                                              | f       | 2010-04-15 21:18:41.583044+00 | 2010-04-15 21:18:41.583044+00 | 2010-04-01 11:25:53.903941+00 |               |            
   16389 | master     |   18043 |       10 | postgres | autovacuum: VACUUM ANALYZE pg_catalog.pg_attribute                                            | f       | 2010-04-15 17:18:36.071479+00 | 2010-04-15 17:18:36.071479+00 | 2010-04-15 16:51:50.230827+00 |               |            
   16389 | master     |   19608 |       10 | postgres | autovacuum: VACUUM ANALYZE pg_catalog.pg_depend                                               | f       | 2010-04-15 16:26:41.941069+00 | 2010-04-15 16:26:41.941069+00 | 2010-04-08 17:08:07.417122+00 |               |            
   16389 | master     |   20278 |       10 | postgres | VACUUM ANALYZE myschema.mytable;                                                  | f       | 2010-04-14 16:24:35.7458+00   | 2010-04-14 16:24:35.7458+00   | 2010-04-14 16:24:28.632431+00 | 192.168.24.63 |       54064
(6 rows)