Ask HN: How effective are third party resume services?

I ask as a job seeker and not as an employer. A lot of companies are using third party resume services like Resumator these days. Are they effective? If so, I assume it is best to just submit my resume as is and let the service determine my suitability. But if they aren't effective, I figure I'll have to do tedious and hackish optimizations, such as plugging as many keywords into a sentence as possible... hopefully this isn't the case.

I'm also curious if using such a service is more of an indication that a company receives too many applications or that they only want the absolute best applicants in the field.