How much should firms invest in social media, and what dollar amount should they expect in return?

It was a question often unanswered, side-stepped or boomeranged back to the crowd during the recent American Institute of CPAs' Practitioners Symposium and TECH+ Conference and the 2012 Association for Accounting Marketing Summit in Las Vegas.

Until Joe Rotella of Delphia Consulting's session on measuring Web site ROI. He explained that firm marketers can't "go to a partner and say, 'We need a new Web site because it needs to be pretty.' Go to them with numbers."

Rotella then presented some of his own, based on the data and subjective calculations of two firm marketers he spoke to about their firm Web presence. When talk turned to social media, however, he acknowledged that these same formulas don't work, making it impossible to know true ROI.

In the "Marketing Masters" session I had the pleasure of moderating, Kevin Bagger, senior director of marketing for the Las Vegas Convention and Visitors Authority, and Carl Cohen, CMO and vice president of marketing for MGM Resorts International -- CityCenter, basically acknowledged as much. "No one can claim to be an expert at social media," Bagger said.

And while Cohen detailed how MGM Resort's Aria Hotel recently invested money to beta test a new Facebook promotional tool that allowed them to track resulting revenue, he agreed.

Bagger recently helped transition the "What happens here, stays here" campaign into the social media age by getting users to sign "pledges" against uploading compromising vacation photos. This is where numbers become more than just "snapshots in time," said Rotella.

I imagine those pledge-clickers would agree.