Actually the main reason Windows Messenger 5 was put on an optional back seat was because of its size and not many people downloaded it, and the new features were for businesses as you said...
Personally I use Windows Messenger 5, for some reason that screwy Windows Messenger starting up in the background signing in over MSN Messenger problem (yes I used Cookies method) didn't stop until I additionally changed to Windows Messenger 5...
There is a chance upgrading to Windows Messenger 5 may fix this, since it is effected...you can download it at
http://download.microsoft.com/download/4/6/c/46cf...0d44df/install.exe