There is a new theory floating around, which I found by way of a thread at Search Engine Watch Forums. The theory is that you can get indexed quickly by placing AdSense ads on your pages. Here is a quote from the original poster "So now you can get into their "index" within 24 hours, free. Just add a little Adsense spider bait to your site."
I personally tested this out on a site. I put up a new site, made sure not to put any links to it. Then I put up AdSense ads and waited. Months later it was still not included in the Google index. Only recently has it been indexed, and I believe that is because someone, somewhere put a link to it. I strongly feel that this theory, although logical, is not correct.
In addition, Google has said that AdSense ads do not affect your listings in Google. They use a totally separate spider to index the site for its AdWords network and a different index. They are separate engines, separate indexes and do not improve or increase your chances of getting indexed in my opinion.