A new whitepaper from Buddy Media called "THE FIVE MOST IMPORTANT METRICS YOU SHOULD BE TRACKING ON FACEBOOK" lists some metrics that don't mean a hell of a lot to marketers who are trying to meet hard quantitative business objectives.
The metrics that Buddy Media suggest you follow are; tab views, engagement, clicks, submits and news feed impressions. I'm sorry but if these metrics don't directly translate into new customers or increases in sales than you're wasting your time.
Tab views and engagements don't mean a damn thing. I am engaged with some brands via Facebook but there is a far distance from being engaged and conversion to a customer. Then there are clicks. What good is clicks if you have a high bounce rate or very low time on site ? The answer to that would be zero !
Finally impression today are worthless unless you're trying to let people know you have a new product or major product announcement.
I have said it before and I'll say it again. "You objectives when using social media should always be either increasing revenue, lowering costs or increasing customer satisfaction. Impressions, clicks and engagement don't mean a damn thing when you have to make numbers to keep management happy. It's about proven ROI and actionable marketing programs not "look what we did on Facebook".