Good question. It would be interesting if the job sites would compile statistics about filling positions they advertise, in the spirit of transparency. My limited personal experience is not positive. I have applied to ads that seemed perfectly tailored to my qualifications, but have never even heard from the employer.

In a thoughtful article on job-hunting, Peter Bregman gives advice on finding a job in today's market. He advises not to spend time on job sites because they are not effective. Instead, work to form personal relationships with those in fields in which your interests lie.

In another article, a blogger recommended niche job sites, such as sites for a particular geographic area or profession, because general job sites are not effective.

Accurate success rates of online job boards are hard to come by in part because large corporate employers do not like to reveal their hiring percentages. A commonly cited independent study published in 2000 reported a success rate of 4 percent. Another study in 2002 found an even lower success rate of 1.4 percent. It appears that time spent combing through online job sites is not well spent.

SOme of them are for real but there are some of them are just scams that's why it is very important tobe careful and picky on the sites you are trusting with

Depends on the industry I guess, I am a software engineer, and I know in my industry it is common practice to advertise jobs that they have no intention if filling through the ad because they already have a candidate. Often times the jobs are advertise with a very specific set of skills that exactly match the candidate they have already selected. Why do they do this, h1b visa requirements. They are required to make sure no american candidate can fill the position, so they advertise a position that fits so few people they are virtually guaranteed no-one fits the description. Then they can go off and hire the cheaper, h1b candidate. This comes from being involved in the hiring of several people at the last company I worked for. I can't speak for other industries however.

It really depends on what website it is.