Since MSN/Live Messenger was discontinued almost a year ago, it wouldn't be a bad idea to remove its field from user profiles and replace it with something that's more commonly used. Perhaps Skype?
It was part of mod package that included some of the other platforms. I'll mention it to our resident SMF expert.
I know that there is a way to do this, I just have to remember how.
EDIT: Found and now disabled. Can't add a new field at this time, but will look into possibly adding Skype in the future, but can't guarantee it.