When clients ask for social networking features on or linked to their web sites, or specify "we want to do social networking," we always have to dig deeper.
Just like with branding, it's not what you think about it, it's what they think about it. And by they we mean everybody else. Do you want your marketing to have meaning? Then find out what is meaningful to your community.
Whether it's a business, a nonprofit cause, or an education institution, community exists whether you're trying to build one or not. It's not always about your product or service or cause, but what makes people passionate about it.
Email lists, group-based networks (like Facebook), moderated forums, feeds, social messaging, video... consider what works for your community (which may not necessarily be what you want to do, or what is convenient).
After all, it's really not your community, it's theirs. It's your role to ensure that they have a place to gather, to communicate, to exchange ideas. A place where they can be inspired, and be informed.