When it comes to making the most money with Adsense you of course have to pick the high paying niches. But simply slapping up some site or blog with marginal content may not give you the maximum benefit that the niche can bring.
Recently there have been alot of people with Made For Adsense Sites (MFA) that have experienced a drop in payouts per click. Many have attributed this to being smart priced by google but there could be another factor in play then Google simply choosing to reduce your earning?
The comment below was taken directly from the Googles Adsense blog and to me is a real eye opener for Adsense publishers that are worried about smart pricing.
From Google Adsense Blog
If your website performs well for advertisers, there may be increased competition among them to fill your ad spaces. This means we'd have a wider variety of possible ads to display, so the ads you see on your site may be more relevant to your site content and your users' interests. This may lead to more clicks from your users, more placement-targeted campaigns geared towards your site, and increased advertiser bids. Overall, you're likely to earn more revenue with your site if advertisers are generating conversions and receiving quality leads from your site.
On the other hand, if your website performs poorly for advertisers, they may be less inclined to display on your site. This means that the ads our system displays on your site may not be as relevant to your site content and your users' interests, leading to fewer clicks and decreased advertiser bids. As a result, you're likely to earn less revenue with your site if advertisers are performing poorly.
From my analysis of this statement it seems that as the economy tightens up and advertising budgets shrink the companies that advertise with Adwords are really analyzing where there traffic comes and how that traffic converts to actual revenue for them.
They are then putting a big emphasis on getting ads onto the best performing sites and filtering out the poor ones. This should be a wake up call to Adsense publishers to build sites with very high quality content and not just some over used PLR or auto generated scraper content because in the long run your earnings will decline.