Crowdsourcing: how do you make online interactivity work?

I’ve been reading several articles advising me to get involved in forums, post comments on other blogs, in order to create community around a blog or brand. Facebook even rates the quality of your page on how many interactions it sees on average over the course of the week.

This raises some questions for me.

• How do you make polls, forums, and other forms of community interaction work?
• How do you make community interaction relevant to your organization, blog, or website?
• When is community interaction actually useful?