Just wanted to give you an update on the UDP issue. During the writing of http://social.technet.microsoft.com/wiki/contents/articles/concern-is-having-outlook-2003-clients-going-to-prevent-me-from-deploying-exchange-2010.aspx, I did a new discovery. Although KB article: http://support.microsoft.com/kb/2009942 stated 10 seconds as the lower limit, the lower limit is actually 5 seconds polling intervals when the “Maximum Polling Frequency” key is set to “5000”.
This has been confirmed with relevant Exchange and Outlook PMs.
The KB article has also been updated to reflect this.
MCM: Exchange 2007 | MVP: Exchange Architecture