People telling you to do the wrong thing is undoubtedly a large problem. For example, one of the things I don't like about the CakePHP framework is the advice you find when searching for seemingly simple questions, like how to use the database's current timestamp with Cake's ORM.

You typically see one of two responses - either call one of your columns "modified" or "created" and hack it in like that. Or, use PHP's built-in date() function, ignoring the issues that brings (e.g. the current timezone could be anything - not always what the database is operating under).

This is an ongoing problem, and is likely related to PHP's ease-of-use; for new users, it's easy to get a sense that you know more than you think you do, and give advice accordingly.

The bigger problem is that it keeps building upon itself. People who don't know better, taking advice at face value, then giving that advice increases the number of people writing crap code. Try searching for password storing advice, and you'll see masses of varients of md5('salty_' . $password);