The idea of formally creating a clan or anything in Diablo 3 right now seems silly; we're not talking MMO levels of team play. On the other hand, it never hurts to have some gaming friends to shoot the time with rather than pugs.
I'm a part of a small gaming group (mostly central/East coast US) with consistent daily activity on our forums/teamspeak in a variety of games. Most of us are waiting on another game's release. In the meantime, several of us (~16 including people who have joined us from here) have jumped into Diablo 3 now and will likely continue playing alongside this other game in the future. We would love to have more people on board to be able to call into a friendly game, or even have some chill people to chat with while farming items for the RMAH.
The overall group is ~50 gamers. Everyone is 18+ (age) with a very heavy interest in PvP (For the other game). In Diablo 3, there will definitely be an interest in PvP, but I expect that the mix between PvE play and PvP will be evenly spread.
There are no "requirements" outside of our general charter, which requires a certain level of respect for your fellow gamers and following the game's ToS (i.e. not hacking). Our main point of contact is Teamspeak 3; there are no plans to house a formal channel or anything of that nature in-game.
If you're interested, feel free to private message me with questions. You can find additional information on our website (registration not required). Our charter in particular, explains more about our gaming ideals and overall group personality (code of conduct, goals, and values).