Developing Online Communities?

Johnny asks: "I'm involved with a project that is looking to develop an online community for technology oriented business customers. Although there are various communities on the web, there is no centralized source of information for the customers. If you could develop an online community to encourage collaboration and information sharing, what features would you want included? How would you go about including features that are widely available in other places (weblogging, message boards, wiki) and generating buy-in from customers."