As it stands right now, the Ads you get from AdSense are keyed to the overall content on your site. This is why most of the ads you will see on my blog are gaming related. Some tech ads are mixed in but, since the majority of the focus of my website (the blog and the main site) are game related, the ads also are game related.
You have probably also seen the numerous websites that tell you "how to make it rich with AdSense." If you have not I'll give you the quick run down:
1) Look for high-dollar keywords. Anything to do with a high dollar class-action lawsuit or lawyers will be your target.
2) Get a bunch of content related to your target. If you are lazy, take it from wikipedia.
3) Upload about 100 pages of this stuff with three AdSense blocks per page.
4) Sit back and collect the money!!!
Now, the best way to make money on AdSense is to find a niche and fill it. My niche is gaming. I focus more on Pokemon here on the blog while my main site focuses on RPG gaming, ala Dungeons and Dragons.
I have a decent click-rate on my site as a whole but my clicks are worth less than a dollar. It's because the niche I fill is not full of high-spending advertisers and I'm fine with that.
When you add in the new Google AdSearch (see it on my right side bar) feature... well... There is a very large potential for abuse.
One could easily put up a website about anything, get AdSense added on and then build the custom search page. Once on the custom search page they can tell their friends to "occasionally" search for things such as... "class action asbestosis law suit" or "DUI law" or "student loans" etc... and then click on the resulting high-dollar advertising links that show up.
With that said, this new search feature may be a method for Google to quickly remove the scammers from their AdSense network.
If they see a site about knitting suddenly pulling search traffic for "congressional lawyers" well, let's just say that they might put two and two together and give that AdSense member the boot!
I'm curious to see what this new feature does for my AdSense revenue. I'm also curious to see how many reports come out of people being booted from AdSense because they abused the AdSearch feature.
I would also like to point out one of the benfits of running this on your website is that AdSense will tell you what your visitors are searching for. This is great in that it allows you to fine tune your website to keep your visitor's attention!
note: I only added this feature today and I did not add the "Search hmtk.com" feature as I could not get it to sit properly in my sidebar. It caused my sidebar to double in width and behave erraticly. This evening I will look over the code snippet to try and figure out why.
The other reason I removed the search of hmtk.com from the Google search feature is that it was not searching my blog as well as my built-in Quicksearch widget does.