Haven't there been lawsuits about a "pervasive" environment of harassment or hostility? It would seem defending against these would require being able to convincingly claim your company was making a reasonable effort to prevent incidents from happening in the first place. I am not a lawyer, though.

I can't speak for the 'official' rules, but the 'off the record' sentiment at the companies where I've worked is the problem isn't so much 'wasting time' by web surfing or offending people but instead the increased resource use (in the case of youtube) and the increased risks of virus infection and corporate espionage associated with some types of surfing. Most of the employees were salaried, and as others have suggested, if they got their work done, no one would make an issue of them visiting ESPN every now and then, or checking personal email at work (even if this is technically against policy).

My current employer does have a passive website blocker (blocks youtubes, which I actually needed for work once, and presumably the social networking sites). That probably cuts out a large number of 'potential temptations', and I'm sure repeated tests are logged. It wouldn't suprise me if a keyword search was occasionally run over the access logs, too, but even that might a stretch. You wouldn't be hired or retained if you weren't basically trustworthy. The block is probably in place to defend against innocent stupidity and forgetfullness.