A 2009 survey commissioned by consulting firm Robert Half Technology reports that more than 50 percent of all US companies now block employee access to social networking sites such as Facebook and Twitter. 54 percent of the surveyed companies completely block such access, while another 19 percent permit it, but only for business purposes. A mere 10 percent surveyed permit social-network use on the job for any kind of personal use; 16 percent allow "limited" personal use, according to the results released Tuesday.