Michael Affronti has posted about Sync filters and performance in Outlook 2007. He also mentioned a KB with a set of troubleshooting performance tips for Outlook 2007 (http://support.microsoft.com/kb/940226).

Performance is one of the most important characteristics of an application for many of our customers in corporate, small business, and personal environments. Since our application is one that many of you spend a good portion of your day in, the development team here is committed to providing a fast and reliable experience every day when using Outlook. Outlook 2007 is packed with new features, but some of our users are hitting performance issues which negatively impact their day-to-day experience. We are now working even harder for our next release of Office to improve the performance characteristics of Outlook across a number of different features and environments.

Read more at source: http://blogs.msdn.com/outlook/archive/2008/03/13/s...e.aspx