newly created database makes queries run 300% faster

Hi,

Alfter hours of adjusting performance of the queries in my Postgres
7.3 database - reprogramming the queries, VACUUMing, changing value of
enable_seqscan - I gived it up, recreated the database and transferred
the dump of the old database into it.
The queries went from 15 sec to 50 msec!! Wow.
Now I would really love to know how the old database got that slow,
and how can I avoid it in the future. Any tips are greatly
appreciated!

Thanks!
Ksenia.