I haven't seen any substantial advances in Longhorn making the computer easier to use for the average user. Just keep in mind that 90% of the users out there aren't able to tell Windows XP from MacOS X. They aren't able to carry out simple tasks like copying a document. The concept of the Explorer or folders & documents escapes them. They aren't able to process all the information presented by today's UIs.
Show me fundamental advances in human-computer interaction for the average user.