As I am based in the Netherlands, I am curious how you look at this issue. I know there are more sites like Simplyhired in the US. If they show all jobs off all companies and become a "one stop shop", how dangerous is that for the likes of Monster and CareerBuilder?
Sites like simplyhired and careerbuilder are generally what I refer to as a "time suck". My assistant sifts through hundreds of resume to find 2. Posting a resume in a job bank, you might as well be a speck of sand on Captiva Island. Especially when you know any savvy employer is using specific key words as bait to catch the right candidate.
More employers are looking at online recruiting marketplaces such as dayak to feed their pond. The fees are lower, they guarantee an employer's money back if the new hire doesn't work out within a probationary period. But sites like that -- the only ones I now use -- are in the strong minority. Just my two cents.
Remember it's harder to find the right job but worth every effort!
Well, just because the aggregator links to the job board, it does not mean that the aggregator doesn't get credit. People will mention they saw it on the aggregator's site, thus increasing its exposure and the employer reconsidering posting with the expensive guys.