Recruiters don't have a magic wand that tells them when new job postings have posted - they get the same information in much the same way as you do (at least the ones I've interacted with). They basically trawl job boards looking for new jobs, then take that one post and throw it up on 10 other sites with slightly reworded text so you can't do a simple Google search to find the original post.

4 months ago when I was job hunting, I came across 6 separate postings from 6 different companies, all advertising for the exact same position. It was incredibly aggravating, because this practice of reposting as many jobs as possible has clogged legitimate job boards to the point that a clear majority of job postings are from "recruiters". There's so much crap you have to wade through to get to any real postings, and that's how they operate. These companies basically impede your job search to the point that you are almost forced to go with them - unless you have patience, a strong dislike for recruiting agencies/agents, and maybe a network of professional acquaintances you can announce your availability to.

Thankfully I have the first two (not the network :( ), and have so far steered clear of recruiters when I find my jobs.

I don't want this to become a pages-long rant, so I'll make the rest short.

I do not know of job boards like Monster have methods to report spam from recruiters. Not only email spam (that I can easily deal with), but phone spam, especially when it's an Indian (it's ALWAYS Indian) recruiter calling me for an AWESOME 3-month opportunity in New Jersey (I'm in Texas).

Most American recruiters I've dealt with have the unfortunate tendency to overstate the salary range their hiring-mark is open to. One of the very few interviews I've had thanks to a recruiter went downhill quickly after I was told the salary range they were going for. This after 3 interviews that I thought had gone splendidly. I was more than a little pissed, and so was the hiring manager after I called him and explained to him exactly what had happened.

Long story short: I no longer entertain any recruiters whatsoever (unless it's an internal company recruiter, of course).