Over at the design community formfiftyfive, they have a great PDF up Christopher Doyle Identity Guidelines 2008 over here (pdf). A clever bit of self promotion from a designer that makes me laugh at the clearance space rules.

There are exceptions (some unavoidable) to the clearance space rule. The most common, and preferred, exception should occur in the company of Sarah_Full Colour Vertical, and ideally Sarah_Full Colour Horizontal.