the one i've used is to create a policy based on the server facet to take a snapshot of the settings of the server after installation to go back and see if anyone on my team, or on any other team, has modified settings which leads to causing problems.
The way we are planning to use policies are to create a production 2005 and a production 2008 policy to see what systems are not up to our current standards, and then implement corrective action to bring them up to our norm.
We are also planning to implement a policy to prevent the creation of stored procedures starting with 'sp%' in our development/staging systems to hopefully curb the practice of developers naming procedures like that.
We are going to couple that together with the use of a central management server, store the polices in the CMS, then group our instances into groups within the CMS and evaluate the policies on the groups of instances.
That is a couple of examples of how we're going to use policies at my company.
Hope that helps,
Steve