For business it is a must, the amount of people on FB who ask "anyone know a good...." instead of doing a search. I also read customers prefer using businesses that have a social media presence as it gives them a direct focal point to complain to or share experiences if things go wrong.
I did it myself on Sunday... I tried to call Virgin Holidays on an 0844 number, I was on hold for 5 minutes and gave up. I made a comment about premium rate numbers and being held in a queue on their facebook page and within an hour I had some representative offering to call me direct.