another thing you can do is analyze the table (analyze table xxx compute statistics) and then look in dba_ or all_tables. (select * from all_tables where owner = 'xxx' and table_name = 'yyy').

you will see stats in there about # of rows, blocks, empty blocks, etc.

If you build a table to store these results every time you do an anlyze (insert into... select * from dba_tables where owner = 'xxx' and table_name = 'yyy') then pretty soon you can see how the table changes over time.

hope this helps,
John