I have found that in most cases, my Adsense based sites make multiples of what any other site generates in revenues. As much as 5 times in some cases.
Having said that, I've noticed that Google is paying LESS these days. I used to get over $8 per click on some ads that today, I'm getting abour $1.25
It's not really Google though... it's the advertisers. They BID for the ads and that bid price is reflected in what we see in terms of PPC Rev. Because of Google's "issues" with Click Fraud (see this article for their "big" coming out announcement:
GOOGLE COMES CLEAN), Advertisers aren't willing to Bid as much for the ads now. It has hurt us all.
As an asidem I've been playing with Yahoo's version of adsense and I guess I have to say that I'm not as impressed with it. The PPC rev doesn't seem any better and in my opinion, the ads aren't nearly as focused or diverse. Either Yahoo doesn't have the advertiser base that Google has or their content engine isn't as good.
Either way, I'm sticking with Google for now. It's apparent that this whole click fraud thing has affected all PPC Rev sites and systems.
Best of luck,
GoPC