From the page:

Google spiders crawl publicly available web information and our index of historic, cached web content. Using a mashup of numerous factors such as recurrence plots, fuzzy measure analysis, online betting odds and the weather forecast from the iGoogle weather gadget, we can create a sophisticated model of what the internet will look like 24 hours from now.

Source: www.google.com.au/intl/en/gday/index.html