I have a theory that agencies like this work relatively well because all the relevant stakeholders are deeply involved in the process, and legislators are not going to do random things to them in order to please some constituency. The more opportunities your agency offers for political grandstanding, the worse run, on average, it will probably be. OPM is not perfect, but from everything I know about it, it does a pretty good job with a minimum of fuss.
But if you bring huge numbers of new people into its purview, that changes. They're going to get a lot more mandates--a lot more contradictory mandates, or mandates that impede the core mission--because suddenly, they're visible.
This article available online at:
http://www.theatlantic.com/business/archive/2009/12/can-the-office-of-personnel-management-handle-a-new-job/31562/
