speeding up inserts

First of all, we are still running sapdb at the moment but are in the
process of moving to postgresql, so it seemed a good idea to post this type
of question here.

In our environment we have transaction processing, each transaction accounts
for 10-30 inserts and 3-4 selects.  We also have users that use a management
interface for doing all sorts of queries on the data once it gets into the
db.  Most of the user queries are selects with a few updates, and fewer
inserts.

The basic problem is that the transaction times are very critical, one
second is a big deal.  The data inserted into the db from a transaction does
not have to happen instantly, it can be delayed (to a point anyways).  Being
that there is only so much you can do to speed up inserts, I have been
testing out a different system of getting the data from the application into
the database.

Now what our application does is create the queries as it runs, then instead
of inserting them into the database it writes them all out to a single file
at the end of the transaction.  This is a huge performance boost.  We then
use a separate deamon to run the disk queue once every second and do all the
inserts.  If for some reason the main application cant' write to disk it
will revert to inserting them directly.

Is this a crazy way to handle this?  No matter what I have tried, opening
and writing a single line to a file on disk is way faster than any database
I have used.  I even tried using BerkeleyDB as the queue instead of the
disk, but that wasn't a whole lot faster then using the cached database
handles (our application runs under mod perl).

Chris