A client recently had an issue with Office documents opening extremely slowly after a migration from SharePoint 2007 to SharePoint 2010. After some questions I was made aware that the issue only occurred in Internet Explorer and had been occurring since they made changes to the group policy.
This eventually led me to the Connections tab of the Internet Options menu. On this tab there is a button for LAN Settings that once clicked opens up a new window and ensure that Automatically detect settings is unchecked. In this case that was all that was necessary to get their office documents opening in a timely manner. Hopefully this will save someone some aggravation in the future.