It should be very easy to tell whether remote workers are doing the wrong thing. Phones have GPS and it's simple to track them. And even more simply... the client paying for his time noticed that he wasn't there and alerted you to that fact.

Things holding us back are the "niceties" like having everyone in one building and being able to quickly call meetings etc. Technology is fixing that problem though (unified messaging etc). BYOD is taking off and companies are realising they can get away with having employees buy their own smart phones. I think the next step will be for companies realising that they can have employees work from home so they won't have to provide office space, parking, air-conditioning etc etc.