The few people who do want to use the wifi maliciously will find creating a fake Facebook account a very minor obstacle to overcome. Therefore, I don't see what benefits it provides to the business.
How about data provided to the business on who their customers are? This seems especially genius in that it doesn't even require the extra step of "checking-in", but can provide the business with the same data.
I agree that could be useful. It's different then the claimed purpose of identity verification for prevention of malicious use, though.