I was a librarian. We did block terrorism/child pornography sites, but beyond that, nothing else. That's because filters can be accidentally over-restrictive. I remember one case where "method" kept getting censored because it contains "meth," or "pocketwatch" because of "twat." If you're looking for dirty words that closely, this falls into the nitpicking category.
Anyway...other than the sites that were blocked nothing else was, and we left it up to patrons to use their best judgment. However, looking at porn in the library still was not allowed. If we caught anyone, we kicked them out on that visit and blocked their Internet access for three months. Then they'd have to ask for it back after and there'd be a big note on their file about porn. Second strike, their access was blocked for good. People can argue "free speech" all they want, but not only does that sort of thing make some people uncomfortable, there were often minors in the library. In the director's eyes, protecting minors was more important than someone's right to watch some chick getting railed.
I don't know if this did happen but apparently they wanted to block file-sharing sites due to bandwidth/computer hog issues. Would have been awesome had they done it while I was there.