Why so long between archive calls?

I am working on getting my development system working with archive logging so I can use the pitr features of Postgres.  However, I am finding that the actual archiving is not keeping up with the generation of the logs.  I am now over 500 wal archive files behind (8+ GB).

What controls how often the archive_command is called?

The actual running of my archive script is taking 1-2 seconds, so I'm not sure why we are so far behind.

Thanks for any advise,

Chris

PG 8.1.3
RH AS 4