UnUsed Tuple Space Huge

From what I understand, the new vacuum will mark deleted tuples as
unused and try to re-use the space if possible. However, I seem to have
a huge amount of UnUsed tuples on some large tables. The table is
updated 1x each day followed by a vacuum analyze.

Any idea why the huge UnUsed tuples. Performance decreases and indexes
stop being used in favor of full table scans.

VACUUM verbose symbol_Data;
NOTICE: --Relation symbol_data--
NOTICE: Pages 767990: Changed 0, Empty 0; Tup 21595176: Vac 0, Keep 0,
UnUsed 16560877.
Total CPU 61.94s/6.94u sec elapsed 179.25 sec.
VACUUM

I'm thinking I may just have to copy/rename periodically to keep it down.

This was on psql (PostgreSQL) 7.2rc2. Will upgrade to 7.2.1, but didn't
see anything in the Changelogs/History to indicate anything will change.

Thanks,
Michael