Is it ROI or IOR?
Kyle Flaherty wrote a post about measuring Social Media the other day. I think its got the priorities straight - it's not only about the financial return of a(ny) tactic, but rather the impact on the business as a whole. For social media: Impact of Relationships.
It would be a bad for business to always pick the tactic or campaigns with the highest ROI. Why? Because measuring a purely financial outcome could result in disjointed, uncoordinated, and contradictory programs. We certainly don't let manufacturing pick their best ROI-project and sales theirs'. We might be making widgets and selling gadgets.
Key Question: As a business, why are we better off implementing this plan versus that plan?
Note: I thought ROI was invented by people trying to figure out where to invest scarce resources. I like Kyle's view better - promoting big-ROI projects got you a bonus and a better job.