Vacuum doesn't end

I have an application that may add a couple million rows per day so I
vacuum nightly. The tables never get to more than about 10 million rows
before I move off the interesting information to other media. Somewhat
often, my vacuums don't complete as shown from this ps command (usually
VACUUMs take a couple minutes)

4442 ? R 949:07 postgres: postgres tag 127.0.0.1(33420) VACUUM

and the CPU for postmaster (hyperthreaded linux) will be in the high
90s.

The locks look like:
scouts=# select * from pg_locks;
relation | database | transaction | pid | mode |
granted
----------+----------+-------------+-------+--------------------------+---------
| | 12826125 | 11642 | ExclusiveLock |
t
16839 | 17230 | | 11642 | AccessShareLock |
t
17251 | 17230 | | 4442 | RowExclusiveLock |
t
17251 | 17230 | | 4442 | ShareUpdateExclusiveLock |
t
17246 | 17230 | | 4442 | ShareUpdateExclusiveLock |
t
17246 | 17230 | | 4442 | ShareUpdateExclusiveLock |
t
| | 12817402 | 4442 | ExclusiveLock |
t
(7 rows)

I all inserts and maintenance through JDBC and may have inserts going on
while a different java thread calls the VACUUM command.

Any thoughts? Can I recover without dropping the server?

Thanks for any help,
Scott