We've used it for a few years ourselves, and we enforce it.
14. REFUSAL OF SERVICE
Hands-on reserves the right to refuse or cancel service in its sole discretion with no refunds. If any of the Terms of Service are failed to be followed, it will result in grounds for immediate account deactivation.
Any abuse of our staff in any medium or format will result in the suspension or termination of your services.
When a user is mad that they deleted a file or they were blocked in a firewall etc and throw various insults at our staff via phone, live chat or emails, then we do warn them to tame the language down. Frustration is understandable, however just as you wouldn't go into a resturant and scream and curse at the person at the cash register, the same goes with online.
Many people have the odd understanding that just because they are behind a monitor they can say and do anything they want - including threats. I wouldn't stand for it in person, and I sure don't stand for it via the web. My staff and my clients are like my family and I protect them as if they were.
We implemented our changes a number of years ago, but it seems to be pretty common place these days.
I can't say I've ever suspended a user for something that they said in a public forum.