I don't go AFK often. I'm usually the "brb" type when I go about something else either concerning other people I'm with or just to handle some business that won't take any time to do. If I know I will be gone for a very long time, I'll either log off or just let people know I'm going to be gone over the hour. I don't like to keep people waiting or having my avatar just sit there with a false promise of my return. Thus, that's why I just log off all together, get whatever I need to do done, and hop back online to enjoy the rest of the day.
Some people have such patience, it's nice.