The Diablo III site has been updated with a new blog post that lays out the details on the upcoming Clans & Communities features that will arrive with patch v2.0.1. Clans will function much like guilds, will require an invitation to join and be limited to 120 members. Communities are much larger and more casual. They can be centered on class, geographic location or any other way that players choose to identify themselves.
The Clan & Community functionality will feature several tabs including: Message of the Day, Roster, Clan/Community Information, and Leader Information. Clans will also have additional tabs: Items, Achievements, Member Joined, Member Left, Member Promoted.
The post also gives players an inside look at how to join Clans or Communities and at additional features that can be found on some of the interface tabs.
Get a look at the entire article on the Diablo III site.