Partiqa: As far as I know, if you have someone on your enemy list, they cannot track you, send you a PM or join any games you have. Other than PB's, they cant contact you.

With Friends, the only real differemce to a non friend is that you can see them "on-line" on the right. I have just made someone who was on my friends list, and selected to put them on enemy's list. They still show up in the "friends Online" - probably because they were on friends before enemies. I know I am on their enemy list and dont see any info re where they are or have the ability to send a message.