I think it depends on if the staff is abusing the privilege and ignoring work or patrons because they are too busy playing online. With smart phones, even if you deny them access on computers, staff could always just use their phone. It makes more sense to allow it, especially if they are doing it during a break and it is not on a computer that the staff needs to do actual work on. The library I work at has not even addressed it as an issue yet. I think it also depends on if staff is logging in and staying logged in and checking it constantly during the day, taking away from productivity and what they should be doing. That's really the bottom line, in my opinion.