A few weeks ago I got a email from this guy who loved a post on my blog. I go by a professional name online and I was scared to reply to him for fear that my actual name would come up. So I went to settings and I tried to change my username. It said that in order to make the changes that I had to authenticate it buy putting in my password which I successfully did. I figured that it worked so I closed my laptop and left the room to get my iPhone. I didn't take long, but when I got back my MacBook asked for the password and on there it showed my birth name. I didn't think much of it so I typed in my password only to find that it didn't work anymore! I tried some other passwords to see if they would work, but none of them did! To make matters worse, I left my email open and I never got to sign out of my tumblr. Should I take it back to the apple store to see if they can fix it? IIN?!

On my PC and phone there's a field for "Your Name" or "Send mail as" in the e-mail account settings. So you can change the name, but keep the address.
My system admin account is completely isolated from application accounts.
What is do though is I have a separate GMail account for online things, which I use from my web browser. (Name set in Account Settings in GMail.)