usually only fixes alignment problems and other CSS related stuff. It doesn't seem to work on deeper issues, like scripting errors and other dynamic issues. At least it didn't solve the issues I had with scripts in IE 8. No one has an answer as to why certain scripting issues came up with basic image viewers in IE 8. I'm sure IE 9 isn't any better at resolving those issues. All they seem to do when releasing a new IE is to create more work for Webmasters.