Some people don’t care for rules when it comes to usability, and with good reason. Not all sites are equal, and more importantly, not all audiences are the same. What’s right for a 15 year old might be very wrong for a 70 year old.
Personally I believe in a hybrid approach, whereby some of the fundamentals of web design should be set in stone, and adhered to. After that, it’s a horses for courses approach, where recommendations trump rules, which are in any case there to be challenged. Apart from white text on a white background of course. That would be stupid.
One of those rules that I would have until very recently placed in my top 25 usability fundamentals would be to avoid horizontal scrolling, at all costs. However, there seems to be a growing trend towards horizontal web design.