E Communication and Privacy.
Your network traffic is very vulnerable to prying eyes. Count on your work web browsing is being logged. Whether those logs are being perused for naughty sites or not is another question. I was on a job once helping with a network analysis and we could see the websites everyone was visiting. There were always pr0n sites on the list, my job wasn't web traffic monitoring so I didn't rat that pr0no-person out we just laughed at it.
At another client site I heard a new hire's first act was to hit a pr0no-site and their second act was to clean out their newly messed up desk and were marched out by security.
Same goes for e-mail. E-mail can be traced and if there is enough reason it can be traced back to you via g-mail, yahoo mail, hotmail, or even bogus return addresses (do you really think the only ID going on an e-mail is what you supply?). Of course if you are calling someone names most likely people will not bother but make death threats and the like and the recipient and authorities may decide it worth the bother.
Don't think hiding behind anonymizers will help either. Again if your e-mail bothers one enough they may be able to appeal to authorities and the like to be able to knock down the wall anonymizers put up.
Just remember, if your note or web use is offensive enough the Internet gives people plenty of clues to track you down.