clarification -
It USED to be true that Excel returned "whatever you typed in when you installed it - could be anything" in response to Application.Username
However, with the advent of 365 and corporate accounts, it's also true that anyone on a corporate 365 account likely didn't type anything in when they installed it, and quite probably Application.Username will return their full name. Depending, of course, on the corporate/user account settings for the Enterprise 365 set up.