Although I have to admit I like avatars and use them on sites where they're allowed, I don't see them as beneficial here on FT. Avatars, especially those with motion, can be very distracting. Plus there are tons of avatars that are XXX-rated and/or insulting and argumentative. And as a moderator I could see this as a problem in trying to decide what was or wasn't allowable.
As others have stated here, a defined group of static airline logo avatars would probably work. But I see FT as a site who's main purpose is to provide information for maximizing points and miles as well as discussing tips, tricks and advice for enhancing our travel experience. And avatars would tend to detract from that discussion IMO.