Online job boards might be most viewed websites these days. With mass layoffs and not much employment in sight there are hundreds and thousands on these job boards scouring through the few jobs and sending resumes to even those with remote possibilities of getting a call back.
How relevant are the job boards in recession?
Of course these job boards help you find the advertised jobs but there is more to these websites. Many of these offer the career tools like resume update help and networking tips.
Here is what I suggest on how to use the job listings on the online job boards:

Time Management First
Time management on the internet must be a priority when searching for jobs.
There are numerous job boards which not only present the current job listings but most of them also offer good career and job search advice; well on that matter there is already an onslaught of information on the web and navigating through the information overload and surfing/reading the articles is a huge task in itself.
You must first work how to be effective at time management on your job search strategies and limit time on the internet. In these times personal approach and interaction might yield better results than sending resumes by hundreds to companies which are already receiving them in hundreds of thousands for one open position.’

Use the Online Job Boards for Research on Available Jobs
Don’t be in a rush to post resumes to 100 different companies; take time to research first.
Prepare a list of those companies hiring in your field / area of expertise and short list those which you can approach at the earliest (depending on their location and if you know of friends who work for this company). Networking is the key to finding jobs during recession. Approach your friends to find out of any available open positions relevant to your expertise and try to get in your resume to the hiring manager/ HR through them.

Narrow down on the Specific Industry
Not all job boards have listings on all industries. For example:

QuintCareers has a great line up of websites where you can find a job or post your resume with one or more of these industry-specific niche job sites.

Job Boards Retarget list
In 2008 had come up with a list of the 2008 Users’ Choice Award winners on the online job boards, listed in alphabetical order by category, read more of this interesting article to see the list.