I think it is credit where credit is due here. The community is slowly resolving the issues we are seeing with Office 2007. I have asked John to log a call with Microsoft so that we can track the issues internally, get bugs issued and get fixes out there. Because any fix we produce has to go through threat modeling and regression testing, we rarely release them with haste unless they are impacting a significant number of users or are a security threat.
However, John has documented many of the problems and solutions, so it is worth a look
19 February 2007 As people start to use Outlook 2007, there is an alarming pattern starting to emerge regarding performance issues when receiving POP3 email. Even the smallest and most trivial of emails can take ages to download and be available, ranging from 30 seconds to minutes. During this time, Outlook and Windows can become slow to respond or become completely unresponsive, usually returning to normal when the send/receive cycle has completed.
Source: Roundtrip Solutions Blog