Best practices for effective_io_concurrency

Hi, All

I read documentation
(http://www.postgresql.org/docs/8.4/interactive/runtime-config-resource.html)
and googled effective_io_concurrency but have not found any expanded
explanation of what it actually is. I feel it rater significant for PG
performance and would like to ask gurus to provide some more
description here. It would be great if someone provide his experience.

Also I've found some info in EnterpriseDB documentation
(http://www.enterprisedb.com/docs/en/8.3R2/perf/Performance_Guide-16.htm).
Is it all actual for PG8.4?

Thank you.

--
Regards,
Sergey Konoplev