You guys post messages on each others "Walls" and become "Friends". I send "whispers" out to "friendlies" so we can "group" and kick some bad guy butt.
You guys send each other sheep or something and play all sorts of games. My character can do the chicken dance.
You guys save up virtual money to buy virtual furniture for your avatars virtual apartment. I auction off self-made gear to get gold so that I can buy myself a giant mountain goat to ride on.
There is one difference though.
My avatar can kick your avatars ass.
I dual wield, BAYBEE!