IMHO they have never been great, but now with a slowing economy it is way too risky to put a resume out there. People are scared to look for a better job right now if their current one is OK. They will come back to all their glory in short order. You are as likely to get rid of Fast Food as you are big job boards: you know the quality is awful, too much of it is really unhealthy, but it is convenient and fast.
Also...more and more Recruiting Professionals keep switching over to LinkedIn, Facebook, Twitter, etc... to use these "alternative" sources. This is flooding those "alternatives" with Recruiters and much of the professional community is beginning to form a disfavorable opinion of those sites.
I am not very active anymore on LinkedIn because I was personally sick of Recruiters trying to connect to me. I would have 5-10 new requests per freaking day and it got old. Random requests for NO apparent reason other than because I was also a Recruiter. Honestly...I don't need 150-200 connections to other Recruiters. That's just ridiculous.
So as you continue to flood these "alternatives methods" what was (again) once niche is now becoming mainstream. How is that any better than the way you were Recruiting before?