I don't hate em. My current job I found through a headhunter, best job I've ever had (paycheck aside).
There is a marked difference though in the quality of them. I've worked with big agencies (RH, Yoh, etc), and they've all been useless. Why? Because they all go quantity over quality, and they have no interest in working with the candidate. They just want to blast over as many resumes as possible for the company to filter through and hire someone so they get their commission.
I've worked with small agencies and headhunters too, sometimes they have the same mentality. But every once in a while you get someone who actually takes the time to do what they're hired to do and actually do the legwork for the company they're contracted out to recruit for, which means taking an active interest in their candidates. It's these guys which I, as an employee, have had by far the best results with. They seem to take an active interest in the company they're getting paid by, so they're the first ones to tell you whether you're wasting your time pursuing the job or not.