TechNet had a great article highlighting What's New In Internet Explorer 8. I learned a few compatibility tweaks to force the Compatibility Mode. Most importantly, the order of what applies as you can set it in many places. This order is sequential, the last applied wins.
- User button in browser
- Group Policy
- Server
- Site
- Page
meta equiv="X-UA-Compatible" content="IE=EmulateIE7"
