Different names?

I was looking at my friends list in-game a few minutes ago, and I noticed that there was a second name after his original one, with () wrapped around it. What is this?

It means that one of your friends is on a different character.
If you add someone to your friends, it will add their account... so if they get on a different character they still show up on the list and the name in () shows you which character it's on (the original character you added is shown, so that you know who it is and don't think some stranger ended up on your list :P)