If you are one of those people that always need to have the latest version of software, if half the software installed on your machine is in beta, or if you are just considering upgrading (or already upgraded) then this post is for you.

You may experience performance problems when you are working with items in a large .pst file or in a large .ost file in Outlook 2007. Short version is that if you have large PST or OST files, Outlook hangs, sometimes 10-12 seconds and may reduce your computer's speed. The cause is "To accommodate new features, Outlook 2007 introduced a new data structure for .pst and .ost files. In this new data structure, the frequency of writing data to the hard disk increases as the number of items in the .pst or .ost files increases."

More info at http://support.microsoft.com/?kbid=932086