The SQL Server 2008 Policy Based Management framework includes views in MSDB to track evaluation history. The syspolicy_policy_execution_history view displays information about when the policy was executed and the results of the execution. The syspolicy_policy_execution_history_details view will display more details including the results of each condition. None of this is very new - and all of this is available in Books Online.
What is interesting - and new in SQL Server 2008 RC0 - is a property which will allow you to configure whether you want to collect all history or only history of failed policies in syspolicy_policy_execution_history_details. By default, SQL Server 2008 will only collect and display history in this view when the policy fails.
To access this option, open Management Studio and select Policy Management in object explorer. Right click on Policy Management to select properties. When LogOnSuccess is set to false (default) successful evaluations are not logged. Setting LogOnSuccess to true will log all policy evaluation results.