I really started this out as a future prospects discussion.
I do think there is a great future in the AdSense Program for people that master the rest of managing an AdSense friendly website.
It's kind of deceiving because it is so easy to install the program, plop down some code and go home. That worked great for a whole bunch of diverse websites in the beginning, not so great now for many folks.
Like most of life, making AdSense work for a site has changed, a lot. The basic install is pretty much the same, but the main issue isn't and probably never has been AdSense. It is everything else that goes in to building and running a successful site.
You need targeted quality traffic and advertisers.
Traffic is something the webmaster has some control over.
The publisher has less, if any, influence when it comes to getting advertisers to use AdWords. I think it can be done, but it's not a plug and play deal like installing the code. It's certainly not as simple as creating content that attracts people ready to pull the "Buy Now" button. That's a big part of it, but you still need the advertisers.
Advertisers can target your site. But they have to have a reason to try it to begin with. We hear a lot about advertisers just skipping the content network all together. That means some great and very productive sites get tossed out with the trash that cause advertiser to skip the content network in the first place.
Can you win those advertiser back, or get them to try your site in the first place? Sure, but it might not be all that easy.
The question is, is it easier and more profitable than selling ads directly and managing those accounts.
In the end, I suspect AdSense will continue to work better and better for some and less and less well for others.
Since the very beginning of AdSense we've heard that it is not appropriate foir every site. I'd say that's more true today than ever before. The range or variety of appropriate types of sites is probably getting smaller.