Microsoft has a closed program; I'm in it. It blows because the advertisers aren't there. I put an MS ad and a Google ad in even rotation over a number of hours on a site, and during that time the Microsoft ad was nothing but crap travel and diet ads. It earned $1.57. The same spot Google ad, which ran the exact number of impressions, earned just shy of a hundred bucks.
Online publishing is not the same game it was even two years ago, and it's not for everyone. If it were easy, everyone would and could do it (though God knows everyone seems to try) You need to *control your business* - not hand it over to Google or anyone else.
Sure, AdSense has peaked for some people, because they haven't changed with the program or with the way online business has evolved. Or their niche is just not as well served by it as it used to be. There've been a ton of changes on the advertiser side too. It has not peaked for me, not by a long shot. It's a tool is my toolbox, and it's just ONE tool. No more, no less.