It mostly depends on the age of the audience who are using your internet services.
If they're 10 or more years of age, you'll probably need a strong filtering system. Otherwise, a weak one will do—most people who are <10 don't use the Internet anyway.
I use K9 as well, and I find it awesome - I tried getting around it, and when I shut it down I had no internet until I rebooted the PC. The only way to get around it is to enter the password. After tweaking the settings (like allowing forums, and blocking certain websites I'm not gong to name), it only shows up when a page is blocked. No 'pay now for pro!' screens. :biggrin: :biggrin:
I use Novell Border Manager for my internet proxy/filter.
It's pretty good, well secured, and fast. http://www.novell.com/products/bordermanager/
But you need the proper networking software for this, i used to use privoxy, but i wanted this to be user based, so i know who accesses what... so lol, i started using this