Paul Boag has written a great blog post about what makes websites successful, and many of his conclusions are directly applicable to social media projects too. Paul says,

Before we can address issues of aesthetics, usability and code, we need to tackle business objectives, calls to action and user tasks. Without dealing with these fundamental principles our clients’ website will fail.

I could very easily rewrite that to refer to social media, without having to change much:

Before we can address issues of social tool choice, metrics and community building, we need to tackle business objectives, calls to action and user tasks. Without dealing with these fundamental principles our clients’ social media project will fail.

Well worth a read, both for businesses considering a website redesign and those considering a social media project, internal or external.