ROB.H  You can also use the free OpenDNS service with which you can either set up your own custom filtering, or choose various levels of automated filtering which are maintained for you by OpenDNS and their contributors. Also you can set it once for your entire network if for example you have 2 or 3 kids, each with their own Mac or PC.  
(Version 4.5.1)

MLIPENK  I downloaded and installed CutX Content Filter for Mac OS X Safari. Then I went into the preferences and selected one of the choice terms that are in the Banned Words list. Next I did a Google search on the selected word. Not only does it do absolutely NOTHING for the quite descriptive search results... the first site I clicked on prompted the alert, with the page content displayed in full debauchery in the background! Granted some sites were actually fully blocked. However, if CutX can't even filter on the Banned Words list, what good is it? I guess it is better than nothing. But for $49 you should get more than a false sense of security. Firefox with the ProCon filter extension does much better than CutX. And ProCon is free. Otherwise Safari's parental controls is still a decent option.  
(Version 4.0.1)

TOMIS  The read me says the program is $99, the Installer says it's $49, trying to register took me to their homepage where I had to hunt around to find the price listed as $49. After the initial setup in the absurdly large preferences dialog they use, I tried it out.

The real advantage of CutX is in it's content filtering. It blocks pages and web addresses which contain banned keywords. This is also its downfall.

I found that on large websites it consistently locks up Safari as it goes through checking every piece of linked media. Additionally, it's not hard to get around the initial blocks by simply running websites through a translation service.

If you are looking to protect young users from inappropriate content on the internet then the solution is MacOS X 10.4's whitelist based parental controls paired with simply being in the room.

The basic idea behind this software is decent. But the implementation doesn't feel professional, and the cost can not be justified.

To sum it up, when CutX blocks a website it display a static page with the words "YOU CANNOT ACCESS TO THIS WEBSITE" in giant letters. I think the poor grammar of this statement is a good metaphor for the program on the whole.  
(Version 3.1)