I’ve been using Outlook 2007 (and the Microsoft Office Enterprise 2007 suite) a little over 2 months now, and if you’re like me you’ve noticed how slow it is compared to Outlook 2003.
Microsoft has known about it and has finally released an update/patch, so install it when you get the chance. BTW, you’ll need to validate your copy of Windows.
If you want to read more about it, here’s an article.