I got my current (awesome) job through a recruiter. I never paid attention to them, except this recruiter:
* was direct and forthcoming with the kind of work, the stage and culture of the company;
* knew exactly what kind of work I did;
* understood the field and could answer my questions.
None of the blanket "Oh hi, are you interested in position <has nothing to do with my line of work." crap. One cold call stating directly the kind of work which was actually relevant to me, said exactly what the position was and the relevant details.
I know plenty of folks (myself included) who have had the exact opposite experience.
Outside of large tech focused firms, your typical HR department doesn't have the specialized knowledge to do tech recruiting. Outside resources and hiring "internal" recruiters has become pretty standard in the SF bay area for small to mid sized firms.
Depends on the recruiter. I've got one recruiter who's a former engineer that's been great (Noah of ScopusIT). I'd also second the FILD "devops" team for good work, although they have less background. I've also worked with some car salesmen types like Talend, which I've been disappointed by (Talend has been especially bad due to their failure to keep good notes)