logging

We would like to log sql activity from our web pages that use postgresql databases.
I read the documentation for 8.1 at postgresql.org. The postgresql.conf file under the -Where to log- section has
#log_destination = 'stderr'
Is stderr the default or do I need to remove the comment symbol to actually start logging to stderr?
Are there recommended settings for all the different items in where to log, when to log, and what to log?

Our goal is to capture errors like when someone claims to have submitted data, yet it is not in the database, and the record count skips an increment-5360 then 5362, missing 5361.

Thanks

Marc