So someone in your organization wants to start using social media, and to be sure that it is worth your time, you need a plan (Mashable”s 5 step plan), and a way to measure its effectiveness or showing its “value.”
Here is a great slideshare on describing social media and developing a plan:
NonProfit Tech 2.0 Blog has a great post about 10 Social Media Metrics for Nonprofit Organizations.
These steps are nothing difficult, and very straight forward, create a spreadsheet to track monthly traffic, views on: your website (unique visitors), your blog, e-newsletter subscriptions, online Donations, activity/comments and fans/followers on your Facebook, Youtube, pages, mentions on Twitter, testimonials, mobile subscribers, and event attendance.
So make your plan, and measure your success!