There were performance issues identified on SQL Server 2005 builds because of the large size of the access cache store on certain servers with huge ad-hoc query workloads. I had blogged about this earlier along with information on how to customize the cache store size using trace flags and registry entries after a certain build of SQL Server 2005.
With SQL Server 2008, we provide access check cache bucket count and access check cache quota size customization through sp_configure. So, if you do need to change these values, you do not have to add trace flags or make registry changes. It is as simple as changing the MaxDop or Max Server Memory on your server.
However, be advised that it is not recommended to change these values unless and until CSS recommends you to do so.