The company's mission is to sell advertising and take care of its shareholders. There's nothing wrong with that. But if you're a job hunter or employer who needs to land a job or fill one, consider this mission statement a disclaimer. CareerBuilder is not in the business of matching people with jobs. It is a marketing and advertising company that uses trivial data base methods to make money from naive job hunters and employers.
Obviously I don't have any insider information on this, but it has a lot of face validity. The corporations are the ones that pay them, they're on the corporations' side. Although apparently they will take my money and bump my "relevancy score". That, to me, is an even bigger red flag: it is impossible to ethically represent two parties with divergent interest: you have to choose one. Taking money from both is an ethical violation, which is illegal in many states (for certain transactions- I'm sure career builders lawyers have look at this).
I don't know if this applies to specialized boards, like dice or Independent School Placement, and I'm sure it doesn't apply to craigslist, which is either free or charges a low flat fee to the employer and doesn't make any claims about helping you. This is also worth keeping in mind when you talk to recruiters- they're nice, but they're paid by the company, not you.