Mostly chatting with each other i guess. Alot of these guilds will be ghost towns till realese. Even more will disband or just never make a piep again. Don't bother with joining one, if you don't want to chat with people. But do join a talkative guild, it can alleviate the strees of waiting for the game xD. And often be quite fun, if it's a guild that plays other things too.