The Symptoms:
You installed SafariBlock and it just doesn't seem to load. Perhaps it used to work, but it no longer does. This symptom occurs either on a fresh install of SafariBlock or after updating Safari to the latest version.

The Problem:
Your user account is part of the "wheel" group, and thus when running Safari it has the same permissions as your user account. MacOSX forbids processes with permissions from the "wheel" group from loading input managers. SafariBlock is an Input Manager, and therefore won't work.

The Tests:
1. open up Terminal.app (search for terminal). Type 'id' (without the quotes) and press enter. You will see a lot of junk, along with your username somewhere in there. Look also for the word "wheel". See it? Then this IS your problem.
2. Optional: create a brand new user - open safari - see if safariblock is working there. (it installs globally, you dont have to install it for this user too). It it works there, but not for you, you likely have this problem.

The Solution:
Follow the instructions here: http://www.macosxhints.com/article.php?story=20071029181159291

That article describes downloading a tool from Apple to let you modify your user and group settings.

You want to locate your own username and remove yourself from the "System Group" (also known as 'wheel' and it has the group ID '0').

Save your changes, restart Safari, enjoy the internet again.