Disclaimer: I do not believe this is in accordance with Google's AdSense terms of service, be warned.
A thread at DigitalPoint Forums describes how you can realize a 500% Increase in revenue from Search. Basically what the AdSense publisher did was pre-populate a keyword within the Google Adsense search box.
Is this legal? Probably not, since you are not allowed to modify the AdSense code in any way.

Comments:
cosa
10/03/2005 12:53 pm
Yeah, it againsts the TOS. But I've once used it (before I realized that it violated the TOS), and it does increase my Adsense for Search earning.
Derek Andrews
10/03/2005 09:34 pm
If it helps increase your revenue, presumably it would do the same for Google. So why not suggest it to them as a feature they could include?