There’s a monster post on the Exchange blog about problems with assigning delegates and/or updating distribution list memberships from the Outlook client.
I can say that we’ve definitely suffered from some of the goofy issues in this article. One item they do not cover is that as a general rule, you should not be assigning more than 4 delegates to your mailbox if you can help it. All too often, people use the delegation feature to work through a business process that can be solved with simple sharing permissions.
But I digress. Here’s the blog post.