If you run a household or small business, you'd probably prefer to keep your users from visiting x-rated and/or malicious Web sites (regardless of whether it's intentional or not). One of the best solutions I've found is ScrubIT, a "filtered DNS" that promises to block pornographic and harmful sites and even fix inadvertently misspelled Web addresses (which can lead users to the aforementioned).
To use ScrubIT, a free service, you simply configure your network router to use ScrubIT's domain-name servers (DNS) rather than those supplied by your ISP. If you're not comfortable poking around your router's settings, there's a small configuration utility that gets the job done (but it's compatible only with Windows 2000 and XP).
Once the configuration is complete, ScrubIT will automatically block any "adult" or potentially malicious sites--over 3 million in all, according to the site. However, you have no control over what sites get blocked, which is the only real downside to using ScrubIT over, say, content-filtering software. If you decide you don't like it, there's an "unscrubit" utility on the FAQ page that will revert your router to its original DNS settings.
This is a terrific solution for parents concerned about their kids' online activities, schools concerned about the same, employers trying to keep the workplace orderly, and so on. In fact, hey, the airlines could adopt ScrubIT for their new onboard Wi-Fi offerings. Just thinking out loud...