PostgreSQL WAL Archiving: Does having archive_mode set to 'on' without copying logs cause performance issues? Using PostgreSQL 8.4/CentOS 6: if I set the archive_mode parameter to on in postgresql.conf, but don't actually store the generated WAL files anywhere via the archive_command parameter, is there any performance impact?

This is for testing the potential for use of WAL archiving on a high-throughput production server: I'm hoping to set archive_mode to on, and set archive_command to something like 

echo `date` %f %p &gt;&gt; archive_log.txt


so that I can monitor how many WAL files would get created during a given time period without actually copying them and risking disk space overruns. Will this affect my server's performance in any way?
There would not be performance impact there.  Your only limitation will be disk space.

Note this is actually used for things like incremental backups and point in time restore.  It's pretty well tested and used.