At my company we're using Team Foundation Server to handle source control and work-item management. After a recent company wide update to Active Directory we ran smack into a flaw in how TFS is designed. 

The problem resides in how TFS handles the history of work items. While it effectively handles the identity of a user despite changes to their AD information, it relies on the "display name" for certain fields within work items. After a change to someone's name, TFS suddenly sees the old name in work items as invalid, and refuses to allow updates to them. While you can update the visible fields fine, there are hidden fields that TFS uses that you can't update. This is a major, major issue that Microsoft doesn't seem important enough to fix before the "resario" release.

Microsoft themselves discusses the issue here: http://support.microsoft.com/kb/932717

While it's not an excuse for such an oversight, they do provide a tool to fix the issue. It's called TfsWitDisplayNames and is available from Microsoft support. They might want to charge a credit card to speak with someone from the TFS support team, but the guy I talked with said he refunds any charges related to this case. If you do end up calling, make sure they do the same for you.

The tool itself seems to work fine (I didn't run into the bug described in this blog though), but it's still a serious pain in the butt to deal with something like this.