This is a known issue with Outlook 2003 clients and Exchange 2010. In Exchange 2010, MS changed the way notifications sent to clients, so if you use Outlook 2003, you might have delays up to 60 seconds to see changes you made in your email folders (delete email, send etc). Check this article - you can change polling interval for old 2003 Outlook clients from default 60 seconds to 10 seconds. It will definitely improve the response time for those who still uses Outlook 2003. Dont't forget to add the registrykey for UDP notifications: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\MSExchangeRPC\ParametersSystem, Subkey: EnablePushNotifications (REG_DWORD), value 1.
http://support.microsoft.com/default.aspx?scid=kb;en-US;2009942
The link provided has been updated by Microsoft to include the latest Update Rollup 3 for Exchange 2010 Service Pack 1. This also answers Dave Kawula's question whether Microsoft plans on fixing for the near future - they have. This rollup re-introduces UDP notifications for Outlook 2003 clients, which resolves most of the performance issues experienced by Outlook 2003 users. Other steps which must be taken with Outlook 2003 users: (1) Must be on Outlook 2003 SP3 (2) Check this knowledgebase article: http://support.microsoft.com/kb/2510153.
For best performance these settings are also recommended (and is come cases required) for Outlook 2003, 2007, 2010:
(1) Within the outlook email profile: enable cached exchange mode (2) more settings, general, automatically detect connection state (3) more settings, security, enable encryption (4) more settings, minimize the number of additional mailboxes in the outlook profile (each additional mailbox, especially large mailboxes, will slow down the client) (5) Remove check mark from "download shared folders" within the outlook profile, more settings, advanced (6) If you're still having issues, recreate the user's outlook profile.
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