In my experience, these recruiters just grep for words like "Ruby" and "Javascript" and blindly send out form letters.
I will say though, when I was looking for a job, a recruiter helped me set up quite a few interviews in a short period, and I ended up being placed somewhere awesome.
I've had pretty poor luck with folks who do out-sourced recruiting, but I recently got headhunted by an in-house recruiter and ended up taking the job and loving it.
I will say though, when I was looking for a job, a recruiter helped me set up quite a few interviews in a short period, and I ended up being placed somewhere awesome.