Here at [RedactedCo], it's in the agreement every employee signs before they get their network access enabled that Internet and email access are for work use; we do have some locked-down 'kiosk' machines set up in the break areas for employees to access the internet from (obstinately to access external sites for benefit-related things such as retirement funds, healthcare, etc.), and for the large part, our employees are actually pretty good about not looking at adult sites.
As the admin of both the internet filter and the email system, I generally don't go on random searches, because a) I'm paid to do other things; and b) there's various rules around it, not to even mention the ethics of looking up someone's browsing history for no good reason.
Most people here are also aware that we use a filtering appliance to both keep people from looking at sites that are malicious, and are productivity sinks. (social media namely, but we do block youtube for some groups of employees.)
Anon to protect my paycheck.